US Aircraft Gun Turrets in RAF Service

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Robert Hurst
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US Aircraft Gun Turrets in RAF Service

Post by Robert Hurst » 27 Jan 2005 12:34

Hi

The Bell Rear Defence Adapter

Both the North American B-25 Mitchell and the Martin B-26 Marauder medium bombers were used in many theatres. These aircraft were fitted with twin-gun rear defence mountings powered by the aircraft's hydraulic system. the guns had a limited movement, but as they were fitted at theextreme end of the fuselage, had a clear field of fire.

The two 12.7 mm (0.5 in) Browning M2 guns were fitted to a powered mounting controlled by hydraulic valves, operated from the usual twin control handles. The gunner sat on a low stool behind an armoured screen, having a rather limited view through the window above the guns, and the sight was mounted on a bracket which was linked to the movement of the guns by a moving rod system. Ammunition was routed from boxes fitted to the fuselage walls behind the gunner in flexible trunking incorporating booster units.

The control handles were mounted on a pillar containing hydraulic valves, which controlled power for the elevation and rotation systems. The position of the panel differed in the two aircraft: on the B-26 Marauder it was located on fuselage wall to the gunner's right, while on the B-25 Mitchell it was fitted over the control handles.

The rear defence position was never manned during take-off and landing. When the position was to be occupied the gunner made his way to the rear end of the fuselage. To cock the guns the armoured panels were swung open, and the manual charging handles pulled back twice (the belts having been loaded before take-off). The guns were then armed and ready to fire. The panels were then closed, and the gunner took his place on the seat. He switched on the main power, the left and right booster motors, and finally the sight rheostat. To either side of the control column were the rotation and elevation bypass valves (A & B in diagram) which were closed, diverting the hydraulic pressure to the control system. Finally he grasped the two control handles so that the bottom edges of his hands depressed the two safety switches (C) - as long as either switch was held down the adapter would move. Under his index fingers were the gun triggers (D). On top of the handles under both thumbs were the press-to-talk buttons which opened the niterphone circuit. In the B-25 the guns could be fired manually: the armoured doors were opened and, using two small tubular handles on the rear of the gun bodies, he could aim, and fire the guns with a trigger mounted on the right handle. In the case of an emergency or on landing, the position was evacuated promptly, the guns were stowed pointing striagh to the rear, the hydraulic valves closed and all switches turned off.

The N-6A or N-8 gunsight was mounted on a long control bracket. The sight could be harmonised with the guns by adjusting vertical and lateral clamping screws. As the compartment was open to the atmosphere, the guns were fitted with heaters, which were switched on. The elctrical and hydraulic systems were then activated, and the turret became operational. When the handles were turned the guns rotated, pressure on the heels of the handles raising the guns, an opposite movement depressed them.

Most of the standard auxiliary units were mounted within easy reach in the fuselage. The locations varied on the B-25 and B-26, but they were always in clear view.

Details of the Bell Rear Defence Adapter

Aircraft Type: B-25 Mitchell, B-26 Marauder
Position in aircraft: Tail
Armament: two 12.7 mm (0.5 in) Browning M2 guns
Gunsights: N-6A or N-8 reflector sight
Ammunition: 400 rounds per gun from fuselage-mounted boxes
Armour protection:
Field of Fire:
Traverse: 30 degrees to each side
Elevation: 5 to 30 degrees to each beam.
Gunfire interrupter:
Motive Power: Hydraulic from aircraft system.

The Bendix Model A and R Mid-upper Turrets

The North American B-25 Mitchell was one of the best medium bombers used by the Allies. Its defensive armament was ceretainly among the most effective.

The upper defence zone was protected by the Bendix top turret. The first Mitchells relied on the Bendix, which was fitted in the rear fuselage for all-round defence, but when two waist guns were provided for later models, the bendix turret was moved forward to a position just behind the pilot's cabin.

The Bendix mid-upper turret was electrically powered by the Amplydine system, in which two infinitely controllable motor-driven generators controlled two drive motors, one for rotation and the other for elevation. The gunner's control handles were mounted inside a metal shield, taking the classical form originated by Nash and Thompson. The two handles were turned to the left for kleft rotation and right for right, while a twisting movement elevated and depressed the guns. At the top of each handle was a high-speed button for rapid movement when changing targets. At the side of the handles were safety levers, grasped with the handles to awitch on the control circuits. Before entering the turret the gunner fitted two heavy ammuntion cans holding 400 rounds each to clips at the side of the centre column, and latched them into position. The ammuntion was then fed from the cans over lead rollers, over cone and guide rollers and into the gun feedways. The gunner could either stand os sit in the turret - footrests were used to stand, or a bicycle-type saddle was clipped down to sit. Either coukld be adjusted to give him a good position behind the sight. He then stooped into the turret, grasped the inner turret supports and pulled himself into position.

On the left side of the fuselage was the main power switch and the heat-light control, which were switched on once the gunner was in position. He then adjusted the sight bulb for brightness by turning the rheostat above his left-hand grip. The safety levers were grasped and the turret was operational. The triggers were under his index fingers, and at the back of the control handle housing were two metal discs which were intercom push-to-talk buttons.

The heated-suit socket, interphone jacks and trouble light were all within easy reach, and any gun stoppages could be cleared. The turret was by no means roomy: once in the turret the gunner was quite restricted in his movements. His field of view was also not ideal, as he could only see to the front aspect, there being no room to turn.
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Post by Robert Hurst » 28 Jan 2005 15:52

Hi

The Bendix Models A and R Mid-upper Turrets

There was provision for hand rotation by means of a hand crank system at the base of the housing, but this could not be operated by the gunner, being provided only for repairs and adjustments.

The gunsight was either the N-6A of N-8 type mounted on a cradle which moved with the guns. The gunsight, cradles and guns could all be adjusted for sight harmonisation in both azimuth and elevation. The guns were usually adjusted to converge at a distance of 914 m (1,000 yds, 3,000 ft). At the side of the reflector sight was a ring-and-bead sight (US 'Iron' sight) which could be used in the unlikely event of both bulbs burning out.

The Bendix Mid-upper turret was only used used in the B-25 Mitchell, which was basically a low-level aircraft in which no oxygen supply was needed.

Details of the Bendix Models A and R Mid-upper Turret

Aircraft type: North American B-25 Mitchell
Position in aircraft: Mid-upper
Model A: rear fuselage
Model R: forward fuselage
Armament: Two 12.7 mm (0.5 in) Browning M2 guns
Ammunition: 400 rounds per gun
Gunfire interrupters: profile-type cut-offs
Gun sights: N-6A or N-8 reflector sight
Field of fire:
Traverse: 360 degrees full circle
Elevation: 82 degrees to the horizontal
Fire control: Electrical solenoid units
Armour protection: Armoured apron to gunner's front
Motive power:Amplydine electrical system
Weight (empty): 326 kg (720 lb)
Weight with ammuntion: 435 kg (960 lb)

The Bendix Model D Chin Turret

As the Eighth US Army Air Force got established in England in 1943, formations of B-17s and B-24s began to hammer German installations in occupied Europe and the German heartland. The Luftwaffe fighter groups soon found ways of attacking these majestic formations, and losses began to mount. A study of the B-17 Flying Fortress had shown that the one weak spot in its defence was from head-on, and a method of attacking was worked-out which was effective, but needed a high degree of flying skill and nerve. The fighter would fly some miles in front of the formation, turn and single out one of the lead aircraft. He would then fly towards it at a closing speed of 805 km/h (500 mph), wait until the last moment, fire, turn over and dive away under the formation. These tactics soon began to tale their toll of the bombers: extra hand-held guns were fitted in the nose by Group armourers, but the force of the slipstream made accurate gunnery difficult. An urgent request was made for some kind of front turret. B-24 Liberators could combat these attacks with their Consolidated and Emerson front turrets, B-17 Flying Fortresses were losing increasing numbers and morale was being affected.

As the Emerson and Sperry companies were fully committed, the giant Bendix Corporation was requested to submit designs for a front defence turret which would not impede the bombardier carrying out his duties. The rapid introduction of the Bendix chin turret was one of the best examples of the strength of American design and production engineering - in a few months Bendix had devised and prototyped a powered twin-gun front turret which was to give intercepting German fighter pilots a nasty shock.

It consisted of a remotely-controlled barbette fitted underneath the nose of the aircraft. The gunner, sitting in a low seat in the nose, manipulated a handlebar controller. The two 12.7 mm (0.5 in) Browning M2 guns were mounted on either side of a central column in which electric motors and gearing controllled gun movement in rotation and elevation.

The gunner stepped into the bombardier's compartment in the nose and sat in the low seat. He reached down to the right of the seat and pulled the car-type seat adjusting lever, moving the seat to suit him. The only part of the turret he could see were the switches, sight and sight cradle suspended from the ceiling. The control handles were mounted on a movable arm stowed against the right side of the fuselage. Directly below were Plexiglass panels, which gave access to the turret mechanism and guns. The guns could be trained and sighted the full 90 degrees of travel, with a little contortion, the seat being fixed to the fuselage floor. The gunner reached down and pressed the control-column release knob, grasped the handles and pulled over the control assembly which locked into place in front of him. Directly behind the control unit on the support arm was the main electrical power switch, which was turned on. On the sight cradle to his front was the sight rheostat, which was adjusted to set the brightness of the aiming display of the N-6A or N-8 reflector sight.

The control handles were grasped, closing the two safety switch levers - the turret would not move unless at least one lever was operated. The turret was now operational. When the handles turned to the left the guns moved left; swivelled away from the gunner at the top, the guns lowered. Under the index fingers were the triggers, and on top of both handles were high-speed buttons, giving an extra burst of speed in changing from one target to another. The guns were cocked by built-in hydraulic chargers operated by a button next to an electrically operated hydraulic valve, pressurising the charging rams. Some later models were fitted with pulley and cable hand chargers, owing to frequent oil leaks on the pipe unions, and to reports that sometimes the chargers would not operate fully.
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Post by Robert Hurst » 29 Jan 2005 11:19

Hi

The Bendix Model D Chin Turret Cont'd.

Each gun had a 365-round can. They were loaded from inside the turret after pushing the seat forward and removing the Plexiglass floor panel. The turret was rotated to the left maximum traverse bringign the left gun and can into position. The can cover was removed and the belt folded inside, with the rounds pointing towards the centre of the turret and over a roller. The gunner repeated the procedure with the right gun, and then went outside the aircraft and removed access panels from where he reached inside and pulled the the belts down through guide rails, under bottom rollers and into the gun feedways.

The gunner's oxygen supply was aituated on the fuselage wall to his left, being fed from the aircraft's system. The heated-suit control box was fixed to the back of the seat, and the intercom kack was held in clips on the right fuselage wall. The turret could be hand operated by cranks fitted into a pinion shaft at the top of the centre column, but these were used only for repairs and adjustments, not for combat emergencies.

Once the guns were charged, the gunner was ready for action. He was, of course, in a more precarious position than an attacking pilot, who was protected by an engine and bullet-proof windscreen. As can be readily imagined, operating the turret against a determined attacker firing a battery of 20 mm and 30 mm cannon was ahair-raising experience. Nevertheless, the Bendix chin turret did much to restore the morale of the Bomb Groups. The first Flying Fortresses to arrive in the UK fitted with the chin turrets were 66 Douglas-built aircraft. These were designated B-17F, but all subsequent aircraft so armed were known as B-17Gs, which was the final and most numerous variant.

After a mission the gunner had quite a lengthy procedure to complete. His duties were as follows:

1. Run the turret into its stowing position - guns pointing astraight forward and slightly p at 26 degrees elevation.

2. Turn off main power switch.
3. Remove Plexiglass floor panel and clear guns by opening gun cover and charging them twice.
4. Remove all ammunition from feedways and ammunition cans.
5. Clean and inspect the gun's receivers and replace Plexiglass panel.
6.Go outside and remove access panels, and field-strip guns.
7. Detail-strip the parts removed from the guns, clean them and check them.
8. Report any malfunctions of turret or guns noted on mission.

Details of the Bendix Model D Chin Turret

Aircraft: Boeing B-17G Flying Fortress
Position: Chin
Armament: Two 12.7 mm (0.5 in) Browning M2 guns.
Ammunition: 365 round ammunition can for each gun
Gun sight: N-6A or N-8 reflector sight
Field of Fire:
Traverse: 86 degrees to each beam
Elevation: 26 degrees above horizontal
Depression:46 degrees below horizontal
Power: geared Amplydine electrical system
Operating Speeds:
Traverse: normal 20 degrees/sec; high speed 40 degrees/sec
Elevation: normal 16 degrees/sec; high speed 30 degrees/sec
Armour: Nil
Weight: 186 kg (410 lb)

The Boeing B-17 tail defence position

The Boeing B-17 Flying Fortress was the backbone of the US Eighth Army Air Force's strategic bomber operations in Europe. An admiral aircraft in many ways, it suffered from being rather tail heavy in flight. This was not a serious problem but it affected the armament installation in the rear fuselage, precluding any power-driven mountings or turrets.

The important tail defence position consisted of a gunner in a rather cramped emplacement behind the rudder. He was provided with twin 12.7 mm (0.5 in) Browning M2 guns on a hand-operated swivel mounting, which was aimed by a ring-and bead (US 'iron') sight fitted to a small tube connected to the guns by a parallel rod linkage system. The gunner had a very limited field of fire, but could deal with any attack mounted from astern.
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Post by Robert Hurst » 31 Jan 2005 12:14

Hi

The Boeing B-17 Flying Fortress Tail Defence Position Cont'd

The Armament system of the B-17E and F was not good, and many improvements were introduced when the B-17G came into service, firepower to the front aspect being strengthened by the Bendix chin turret. Problems with the ball turret were resolved, and a modified rear defence cupola was provided. Known as the Cheyeene turret, it had a vastly improved field of fire, the guns being sighted by a reflector sight, the N-6A, in place of the ring-and-bead. Although other experimental tail defence positions were designed for the B-17, the Cheyenne was thwe final modification to reach the Bomber Groups, and was also used by RAF Coastal Command and No.100 Group.

Details of the B-17 Tail Defence Turret

Aircraft: Boeing B-17E,F and G Flying Fortress
Position in Aircraft: Tail
Armament: two 12.7 mm (0.5 in) Browning M2 guns.
Ammunition: 200 rounds per gun.
Gun sight:
B-17E, F and G (early): Ring-and-bead (US 'iron') sight
B-17G (late production): N-6A reflector sight.
Field of fire:
B-17E, F and G (early):
Traverse: 30 degrees to each beam
Elevation: 40 degrees
Depression: 15 degrees
B-17G (late production)
Traverse: 80 degrees to each beam.
Elevation: 70 degrees
Depression: 40 degrees
Armour protection: Nil.

The Briggs-Sperry Models A13, 13A and A2 Ball Turrets.

When the prototype of the Briggs-Sperry ball turret proved to be an ideal (if unconventional) design, it was specified for both the B-17 Flying Fortress and B-24 Liberator. It was equipped with the ungainly but useful Sperry computing gunsight, which used the same principles for predicting deflection and ballistic trajectories as the much larger anti-aircraft predictors. It was the most compact turret in service, the gunner crouching behind the sight with his knees up on either side. This was not quite as uncomfortable as it sounds, and the gunner had a reasonable field of view to his front and side. Ball turret gunners were necessarily small but built for heavy duty. They were usually between 1.625 m (5ft 4 in) and 1.676 m (5 ft 6 in) tall.

The B-17 Flying Fortress installation was straight-forward, being a ring fixed to a strengthening unit in the fuselage floor suspending the turret frame. However, the B-24 Liberator had only a small ground clearance, and Sperry designers were instructed to make the turret retractable into the fuselage. This proved an interesting exercise, as can be imagined: it was finally suspended from a heavy roof support by a hydraulic retraction ram which swivelled through 360 degrees.

The turret was hydraulically controlled from a Vickers Inc. Power unit. This worked on the same principle as the Boulton Paul system, in that a constant-speed electric motor was used to power two hydraulic pumps, the output of which was controlled by handgrips, to drive the rotation motor and elevation rams of the turret and gun cradle. The speed and direction of the elevation rams, and the azimuth hydraulic motor, were varied by the amount of movement of the hand grips controlling the hydraulic valves. The hydraulic glands were prone to leakage - sometimes gunners were soaked with unpleasant and highly inflammable oil. This problem was partially solved on late models, but never completely prevented.

The turret of the B-24 was fully retractable, being extended as follows: The guns were lowered to 90 degrees vertically downwards by a hand crank until the access door was uppermost and closed. The hydraulic retraction valve was closed, power for retraction being supplied by a hand pump in the fuselage, which was given a few strokes to lift the suspended turret off the safety hooks, which were then disengaged. The hydraulic valve was then slowly opened, allowing the turret to descend under its own weight until tapered bushes seated in their housing. The master switch on the support beam was then turned on. Getting into the Sperry ball was a delicate operation, for unless securely locked, the delicately balanced unit could swivel round and break a man's leg. The gunner had to open the door, and use the hand crank to steady the turret, whilst reaching inside and moving the elevation clutch to 'out'. After trying his right foot on the seat to ensure no movement, he lowered himself in by grasping and swinging down on the support frame. He then put his right foot in the right foot-rest, and his left heel on the range pedal. After fastening his belt he closed and fastened the door.
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Post by Anwar bin Zapari » 31 Jan 2005 15:35

Nice, real nice...

Signed,
Anwar

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Post by Robert Hurst » 02 Feb 2005 14:29

Hi

The Briggs Sperry Models A13, A13A and A2 Ball Turrets Cont'd.

To get out, the guns were pointed straight downwards (this was indicated on a dial), the doors were opened, and the gunner extricated himself. He closed the hydraulic valve and, using the hand pump, raised the turret until the safety hooks could be engaged. Then, using the hand crank, he raised the guns to 22 degrees. A cam-operated switch closed when the turret was correctly retracted, and flashed an indicator light in the pilot's compartment to tell him the turret was stowed.

To get out, the operation of the B-17 Flying Fortress version was identical except, of course, that there was no retraction system. Nevertheless, it was essential to point the guns rearwards when landing or taking-off, and under no circumstances were gunners allowed to occupy the ball turret during this time. Once the Liberator turret was extended there was always the risk that the retraction mechanism could be damaged or become unserviceable. If this happened the turret could be retracted by using the aircraft's bomb hoist. This was a difficult two-man operation but it could be accomplished in an emergency.

Once seated, the gunner prepared for action. He checked that the rotation power clutch was engaged, turned on the sight switch, and grasped the handgrips. The controls operated opposite to all other turrets - to rotate to the left, the handles were turned to the right, and vice versa; to elevate the guns the handles were pulled towards the gunner. The guns were fired by thumb buttons on each handle. The guns were charged by pulling two handles next to the gunner's feet: he crossed his hands and pulled the right gun charging handle with his left hand, and the left one with his right. He plugged into an oxygen socket under his seat, and his interphone plug to a socket to his front. By his right foot was a turret rotation dial. He could turn the turret by a hand crank high to his right, the elevation handle for hand control being to his left.

The Sperry K4 sight was then checked. The gunner would have heard the sight drive motor start when the sight switch was closed. He now looked into the viewer, and adjusted the rheostat until the reticle suited the outside light level. The sight gave a point of aim, calculated from range input from the left foot pedal, and turret movement via flexible shafts connected to the turret mechanism. When a target was sighted the gunner set the wing span on a dial, tracked the target and used his left foot to frame it between the aiming reticles. As he pressed the buttons the guns fired, drawing the ammunition belts from the tanks above his head. The tanks held enough ammunition for 30 seconds' firing, usually used sparingly.

Luftwaffe pilots approached the underside of US bombers with great care and not a little apprehension. The ball turrets proved to be the only really effective under-turrets, for they gave defensive fire covering the complete lower hemisphere.

Details of the Briggs Sperry Models A13, A13A and A2 Ball Turrets

Model and Aircraft:
Model A2: Boeing B-17E, F, and G Flying Fortress
Model A13 and A13A: Consolidated B-24H, J, M and N Liberator
Motive power: Vicker hydraulic system
Position: Under-fuselage
Armament: Two 12.7 mm (0.5 in) Browning M2 guns
Armour protection: Armoured seat back
Fire control: Magnavox solenoids
Field of fire:
Traverse: 360 degrees
Depression: 22 to 90 degrees
Gunfire interrupter: Profile type cut-outs
Ammuntion:
Left gun: 570 round top ammuntion box
Right gun: 450 round bottom ammunition box
Gunsights: Sperry K4 Computing sight
Turret speed: 30 degrees/sec
Dimensions:
Diameter: 1.1m (44 in)
Distance below fuselage: 0.6m (24 in)

The Consolidated Models A6 and A6A Nose and Tail Turrets

These hydraulicaly powered turrets were fitted to some B-24J Liberators. The Model A6A tail turret was found to be so successful that the Consolidated designers were asked to adapt the design to fit the nose section of the B-24. The installation was accepted for production, having the added advantage of an almost identical parts list, which enabled Group stocks to be reduced. It was found that there was no room in the nose position for the self-contained hydraulic power unit, and pressurised oil was fed from the main system of the aircraft. The tail turret power unit consisted of a 24 volt shunt-wound motor driving a spur gear pump working at 83 kg/sq c (1,200 lb/sq in). A relief valve opened when pressures of over 91 kg/sq c (1,300 lb/sq in) were reached, exhausting the oil to the return flow. A pressure switch on the dleivery line brought in the pump when the pressure dropped below 77 kg/sq c (1,100 lb/sq in).

The pressurised oil was fed into an accumilator consisting of two halves, one of which contained the oil. The other was joined to the first by a rubber diaphram and was pumped to 42 kg/sq c (600 lb/sq in). With compressed oil, this kept a constant pressure to the turret and compensated for oil used in the elevation ram.

The Consolidated turrets were rotated by a multi-plunger fixed-displacement variable-speed hydraulic motor, worked through a gear train which operated a cable drum. two wires were wound round the drum in opposite directions, the end of each being fixed to the turret drum. When the motor was actuated one cable wound as the other unwound, rotating the turret. The gun cradle was elevated by two hydraulic jacks controlled from valves on the gunner's control handles.

The gunner was protected to his front by a bullet-proof glass panel 52 mm (2.2 in) thick. Directly below this was a 22 mm (0.8 in) armour panel, and to the right and left of the gunner's knees were two more small panels each (3/8 in) thick.
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Post by Robert Hurst » 03 Feb 2005 12:44

Hi

The Consolidated Model A6 and A6A Nose and Tail Turrets Cont'd

The two 12.7 mm (0.5 in) Browning M2 guns were mounted on trunnions on either side of the gunner, each being elevated by a hydraulic jack. The tail turret guns were sometimes found to be out of alignment after traversing to the beam position, the slipstream acting on the outer gun straining the mounting. An adjustable tie rod at the muzzle end of the barrels overcame this problem, and also assisted in harmonising the two guns. Ammunition was supplied from two boxes in the fuselage, the belts being pulled into the guns by powered sprocket boosters. The belts were routed up between the guns, over feed chutes and into the feedways, the first link of each belt being fitted to its receiver just before take-off. The 400-round boxes gave the gunner 30 seconds' firing , usually ample for an operation.

it is not generally realised that entering a turret such as the Consolidated could be a very hazardous procedure. Entry always took place when the aircraft was in full flight, and being a very finely balanced enclosure, if the lock was taken off, any change of altitude could whip it round and trap anyone entering.

Before entering the turret the gunner switched on the electrical mainswitch, which was outside the turret on the fuselage wall. He then opended the doors and reached inside to make sure that the main hydraulic shut-off valve was closed - if it was open the slightest touch on the control handles could seriously injure the gunner when the turret rotated. He then checked that the elevation bypass valve was closed - this was a small handle under the control unit. Grasping two handles above the doorway he swung both feet into the turret pit and settled into the seat. The doors were then closed by pulling a red knob to his right, which operated a cable which closed and latched the doors. The oxygen supply was situated near his left shoulder, while the heated-suit control box was on the turret wall to his right near the interphone jack box. A trouble light and switch were fitted in the upper right-hand corner of the turret, and on the left forward wall was a warning bell which was rung by the pilot when the turret was to be evacuated. On either side of the seat were two shafts for manually operating the rotation and elevation drives: the handles for these were stowed in clips on either side. Close to the gunner's feet were two pedals for firing the guns in manual operation.

Once settled in his seat the gunner made the turret ready for action. He first turned on the main hydraulic valve and removed the rotation and elevation locks, the lock handles being stowed in clips on the wall. He then turned on the power switch near his left knee, and on the same panel he switched on the booster motors and trigger switches. The sight was switched on and the brightness of the aiming graticule adjusted with the rheostat, He then cocked the guns -the charging handles were on either side of the bullet-proof glass to his front - and reaching forward he grasped the two handles and pulled them back sharply. Holding the two handles of the controller. he tested the rotation and elevation movement. After crossing the English coast he would fire two short bursts after warning the pilot. From now on he would be searching the skies for little dots that could quickly turn into attacking fighters.

Details of the Consolidated Model A6 Nose and Model A6A Tail Turrets

Aircraft: Consolidated B-24J Liberator, Consolidated PB4Y-1 Liberator
Position in aircraft:
Model A6: nose
Model A6A: tail
Armament: Two 12.7 mm (0.5 in) Browning M2 guns
Ammunition:
A6: 400 rounds boxes in turret
A6A: 600 round boxes in fuselage
Gunsights: N-6A Reflector sight, N-8 Retiflector sight
Field of fire:
Traverse:75 degrees either side of centreline
Elevation: 71 degrees above horizontal
Depression: 45 degrees below horizontal
Armour protection:
52 mm (2.2 in) bulletproof glass panel and 22 mm (0.8 in) armour plate to gunner's front.
Motive power:
A6: hydraulic pressure from a/c system.
A6A: integral motor driving hydraulic compressor.
Firing mechanism: Magnovox solenoids.
Turret speed: 40 degrees/sec.

The Emerson Model Model 111 Tail and Model 127 Nose Turrets

In 1941 reports of the air war in Europe began to show that bomber aircraft of both the Luftwaffe and the RAF were proving very vulnerable to fighter attack.

The US Navy Bureau of Aeronautics formulated a crash programme and brought in the Emerson Electric Manufacturing Company of St Louis to produce turret designs based on the Boulton Paul Types S (tail) and T (dorsal), armed with twin 12.7 mm (0.5 in) Browning guns. These turrets had been converted from 7.7 mm (0.303 in) designs and were not fully developed. Working strictly to the Navy contract Emerson built a dorsal turret based on the BP Type T, and then proceeded to modify it for satisfactory operation. The prototype turret was submitted for evalution by the Navy in the summer of 1942, but it was found to be unsuitable, due to (a) poor control and operating characteristics; (b) insufficient room for the gunner; (c) poor scanning facilities; (d) excess weight: and (e) lack of consideration of American installation requirements, available space, etc. The Emerson Model ANB-101-115 was obviously not a succcess.

Whilst the work was proceeding, the Armament Laboratory tested a two-gun mid-upper turret submitted by the Airarms Company, a subsidiary of Lockheed's vega Aircraft Company. This turret was again loosely based on the Boulton Paul design but was more roomy and better engineered. nevetheless. although the Armament Laboratory were anxious to make use of it, it was far from perfect.

Emerson were asked to modify the turret, making use of standard AAF recoil adaptors, gunsights, etc and install the Amplydine electrical drive system. The new turret was submitted for testing and proved satisfactory on ground trials, so it was then installed in a Lockheed-Vega Ventura aircraft. Once again the company was informed that the turret had basic problems - the available Amplydine power units gave insufficient power, and from a manufacturing point of view the design was not sound.

The first Emerson design contract was for a pressurised ball turret, the Model 110, which was started in early 1942 and completed in September. Special features incorporated included a pressurised structure for high-altitude operation, self-contained pressurising blower and regulator valves, more room and comfort than the Sperry ball turret, and it was compatible with the B-29 aircraft. When the B-29 armament was fixed as a remote control system, the promising Emerson Model 110 was killed off. The company was by this time manufacturing the Sperry ball turret, although it considered its own Model 110 to be superior, for it would have saved weight and cost.
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Post by Robert Hurst » 09 Feb 2005 13:10

Hi

The Emerson Model 111 Tail and Model 127 Nose Turrets Cont'd

The Model 3 Tail Turret

The first tail defence system of the B-24 consisted of a crude twin-gun mounting. In the spring of 1942 Emerson was asked to design a fully enclosed power turret to replace it, which was to be the Emerson Model 111 tail turret. The project was given priority over all other work, and in August a turret was produced using experience gained on the previous abortive designs. It proved superior to anything produced in the USA up to that time. The turret was received with enthusiasm by the Armament Laboratory and Eglin Field, where representatives of the Navy and Army were given demonstrations. The aircraft companies were not so keen, due to the weight of the turret, but these objections were overruled and the Model 111 was accpeted in all future B-24 aircraft. At about this time the company was asked to look into the possibility of converting the Model 3 into a nose turret for the same aircraft. Although the ensuing design did not fit smoothly into the nose stucture, it was a thoroughly workmanlike design and proved a success, becoming the Emerson Model 127. B-24s fitted with this nose turret in place of the usual glazed nose became B-24J Liberators. In RAF service these aircraft were known either as the Liberator GR.Mk.VI when used by Coastal Command or Liberator B.Mk.VI when used by Bomber Command. The company went on to produce many more turrets, mostly for developments of the B-24 and B-29 aircraft.

Operating procedure Emerson Models 111 (tail) and Model 127 (nose) turrets

Ensure the external power switch (on the fuselage wall) is open. Open turret doors and check that all switches are off, this ensures that you will not become trapped if any controls are touched whilst you get in. Grasp the hand hold above the door, swing both feet into the turret bowl and slide into the seat, close and latch the doors.

Turn to the switch box over your left shoulder. First turn on the master switch, wait a few seconds, then turn on the elevation drive switch. Lift the guard and turn on the gun switch, then grasp the control handles in front of you, using the bottom of your hands to press down the two safety switches which act as dead man's handle. Turn on the sight rheostat, and adjust the brilliance of the light.

To operate the turret turn the handles as you would a bicycle, right to go right, left to go left. Rotate the handles towards you to elevate the guns, away from you to depress them. The gun triggers are under your index fingers, and on top of the right handle is the high-speed button, this throws the turret into high speed for changing from one target to another. On top of the left handle is the push-to talk button, this opens the interphone system for you to speak. Near your knees are the gun-charging levers, these cock the guns, pull them up sharply, then let them drop back. All important electrical circuits have resettable circuit-breakers. Your oxygen is supplied from a demand-type regulator, together with a flow and pressure gauge. Your heated-suit plug is near your right foot, and the microphone is plugged into a socket on the control-handle column. The guns can be fired by a foot firing pedal, if your hands are occupied. The Emerson turret has an emergency rotation control which enables you to be helped out if hurt. A cable is pulled from outside in the fuselage, this disengages the power system, then, by using a crank handle kept on a bracket beneath the door, a shaft can be turned which will centre the doors to open them. The N-6A reflector or N-8 retiflector gunsight can be harmonised to the gun by adjusting bolts, to do this you will need a boresighting tool. Ammunition is brought into the turret from external boxes, the belts being taken in through a hole in the floor. The belts are fed up through a chute double link ends first, into the gun feedways, cock the guns twice and the turret is ready for action. Always remember to stow the guns looking foward in the nose turret and to the rear in the rear turret. Never occupy the turret during take-off or landing, as quck changes in speed make a turret a dangerous place at those times.


The Model 127 nose turret was identical to the Moddel 111 tail turret, although the installation was not the most aesthetic or streamlined enclosure ( it was said to reduce the aircraft's speed by 13-16 km/h (8-10 mph). It proved popular with crews and became standard on production lines not using Consolidated turrets.

The success of the turret can be seen by the fact that no less than 12,000 were produced by the company. In order to prevent any delay to bomber production, a consoderable force of Emerson mechanics was assigned to the giant Ford plant at Willow Run, to prevent any delays in converting the B-24s on the lines to the new turrets.

Details of the Emerson Models 111 Tail and 127 Nose Turrets (US Army Type 15 Turret).

Aircraft: Consolidated B-24H and J Liberator
Position:
Model 111: Tail
Model 127: Nose
Armament: two 12.7 mm (0.5 in) Browning M2 guns
Ammunition: 500 rounds per gun from external boxes
Gunsights: N-6A reflector sight; N-8 retiflector sight
Field of fire:
Traverse: 75 degrees either side of centre
Elevation: 60 degrees above horizontal
Depression: 50 degrees below horizontal
Armour: 51 mm (2 in) bullet-proof glass moving with guns; 1 mm (5/8 in) and (3/8 in) armour plate below.
Drive: 530 watt Amplydine electrical
Operating speeds:
Traverse: normal speed 20 degrees/sec; high speed 45 degrees/sec
Elevation: normal 16 speed degrees/sec; high speed 30 degrees/sec
Structure: The Model 111 was the first turret to use cast magnesium for principal structural items.

The General Electric Boeing B-29 Superfortress Remotely-controlled Armament System.

The Boeing B-29 Superfortress was the most advanced bomber used by the Allies, being exclusively operated by the US Army Air Force in the Far Eastern war zones. This aircraft was armed with remotely controlled barbettes, fitted with multiple 12.7 mm (0.5 in) Browning guns.

It played a leading role in the defeat of Japan in the Second World war, first by heavy fire-bombing attacks, and finally by dropping the two decisive Atomic bombs. Superfortresses also took part in the Korean war. During this conflict 16 B-29s were lost to MiG attacks, but B-29 gunners accounted for 33 Communist aircraft, 16 of which were MiG-15 jets. Although the aircraft was only used post-war by the RAF as the Washington B.Mk.I its unique armament systems justifies its inclusion here.
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Post by Robert Hurst » 11 Feb 2005 14:40

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The General Electric Boeing B-29 Superfortress Remotely-Controlled Turret System Cont'd.

The initial armament scheme was to be based on the Sperry periscopically sighted turret system, but after disappointing trials of these turrets the USAAF specified the new General Electric remotely controlled turret system, in which gunners seated at nearby sighting stations aligned specially linked gunsights with the target. Having no occupants, the designers were able to keep the profile of the turrets down to the minimum required to accommodate the guns and ammunition. The turrets could be trained to deal with attacks from any quarter not in line with the airframe.

There were five sighting stations: one in the nose, one behind the tail, two at waist positions, and one in the mid-upper position. At each sighting station was a gunsight, manipulated by either twin control handles similar to a normal turret or, in the case of the side hatch positions, two control knobs fitted to the sides of a pedestal, on top of which was the gunsight.

The sight was linked to the turret by two Selsyn generators, which sent a stream of electrical impulses to the turret. These signals indicated the position of the sight in relation to the Selsyn generators on the turret. If the gun mountings in the turret were not in alignment with the sight, a signal was sent to a servo amplifier by the control transformer, the strength of this signal being proportional to the difference in alignment. The servo amplifier received two sets of signals - one for elevation and depression, the other for azimuth (rotation). These signals were amplified and converted into direct current, and sent to the field-windings of an Amplydine generator. The armature of the Amplydine received a constant 27 V DC supply from the aircraft DC generator. The variation in current from the Selsyn generator to the Amplydine field-windings varied the speed and direction of output of the Amplydine generator which energised the turret drive motors, lining up the gun mountings with the sight. By this method the gunner controlled the alignment of the guns. The response of the system to the movement of the sight was immediate, and a central computer adjusted the alignment of the guns for range and bullet drop.

The armament of some of the B-29 turrets was changed during its operational service. Early production models carried a 20 mm (0.79 in) M2 Type B (US Hispano) cannon in the tail turret, but this was found to restrict the field of fire and was soon deleted, leaving just two 12.7 mm (0.5 in) Browning M2 guns on all main production aircraft.
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Post by Robert Hurst » 11 Feb 2005 15:18

Hi

The General Electric Boeing B-29 Superfortress Remotely-Controlled Turret System Cont'd.

The tail turret was the only position where the gunner was not remote from his guns. He operated the turret by control handles which energised an identical system to the other turrets, but with direct sighting. The other four turrets were all remotely controlled, as previously described. These turrets were fed from large curved ammunition boxes loaded with 925 rounds for each gun, the ammunition belts being pulled up into the guns by powered sprockets. The turrets were quite weighty, the four-gun upper turret weighing 879 kg (1,938 lb) fully loaded, plus the gunner and his controls.

Each sighting station had primary control over certain turrets: the front position controlled the upper and lower front turrets, the top position controlled the upper aft turret, the bottom position controlled the lower aft turret, and the tail position controlled the rear turret. During an attack, gunners could pass control of their turrets to other sighting stations as a target moved out of their field of view: in this way the front gunner could pass on to the top and side gunners, while the tail gunner could pass on to the side gunners.

In common with many features of the B-29 Superfortress, the armament system had many teething troubles, mainly due to rushed production and inexperienced installation engineers. Gunners needed a four-month course to become competent, and even with such an advanced armament system many B-29s were shot down over Japan, 13 being lost over Tokyo on 13th April, 1945. Nevertheless, using firestorm tactics similar to RAF area bombing, many Japanese cities were devastated before the Atomic onslaught.

Details of the General Electric RCT Armament System

Project leaders: General Electric Company (turrets: Emerson Electric).
Aircraft: Boeing B-29 Superfortress
Position in aircraft and armament:
Front upper: Two or four 12.7 mm (0.5 in) Browning M2 guns
Front lower: Two 12.7 mm (0.5 in) Browning M2 guns
Rear upper and lower: two 12.7 mm (0.5 in) Browning M2 guns
Tail: Two 12.7 mm (0.5 in) Browning M2 (early versions had additional 20 mm (0.79 in) M2 Type B cannon fitted) guns.
Ammuntion: 925 rounds per gun
Field of fire:
Rear:
Traverse 30 degrees each beam
Elevation: 30 degrees
Depression: 30 degrees
Uppers:
Traverse: 360 degrees
Elevation: 90 degrees
Depression: 5 degrees
Lowers:
Traverse: 360 degrees
Elevation: 5 degrees
Depression: 90 degrees
Power system: Amplydine electrical by Central Station Fire Control system.
Dimensions:
(all but tail)
Diameter of cupola: 1.2 m (48 in).
Overall height: 1.7 (68 in).
Weight:
Front upper: 879 kg (1,938 lb) fully loaded
Others: 612 kg (1,350 lb) fully loaded.
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Post by Robert Hurst » 12 Feb 2005 11:14

Hi

The Grumman (Emerson) Models 150 SE-1 and SE-2 Mid-upper Turret

In the later war years, the Fleet Air Arm used the Stocky Grumman TBF Avenger for torpedo, strike and reconnaissance operations. This aircraft was defended by a tunnel gun under the rear fuselage and a mid-upper turret. The turret was produced in two models, the Grumman 150 SE-1 used in the TBF-1 and 150 SE-2 used in the TBF-3. As the gunner also acted as an observer, the turret was fitted with a single 12.7 mm (0.5 in) Browning M2 gun, leaving room for other equipment and providing an adequate field of view for sea searching.

The Model 150 SE-1 was electrically powered and had a high-speed facility. It was controlled by a pistol-grip control incorporating a squeeze-lever safety switch. To move the turret the pistol grip was pointed to the direction required. The high-speed button was thumb-operated at the top of the grip. When the safety switch was released, the gun automatically returned to a position trailing aft and cut off the drive motors. Under the index finger was the trigger, the gun being charged manually by a handle pulled with both hands.

The gunner's oxygen was fed from the main aircraft supply through a rotating gland at the bottom of the turret. the interphone box was near the gunner's left knee, and this also contained the radio volume control and wave band selector.

In an emergenmcy the gunner could leave the aircraft through the side of the turret. The large circular Plexiglass side frame could be jettisoned by turning a handle in the centre; it could then be pushed out leaving a a hole big enough for the gunner to escape. The gun was sighted by a Mark 9 (based on the British Mk.IIIA) reflector sight, with a Mark II ring-and-post sight as standby.

The ammuntion can was fixed directly under the gun. To remove the can the turret was brought to the stowage position facing aft. The can was released by pulling a small yellow knob under the gun bracket. The installation of the can was done from outside, where it was clipped onto a guide rail, pushed inwards and fixed into place by a cable-operated lock. The can held only 200 rounds, enough for 15 seconds' firing - sufficient to counter two fighter attacks or strafing operations.

After extensive operations the US Navy Bureau of Aeronautics suggested that extended range and payload could be achieved if the Avenger could dispense with the gunner. It was suggested that a lightweight turret could be fitted and manned by the radio operator. He was to be provided with a rotating platform, with a sling-type seat for extended periods of operation. The 'Stand-up type Navy Turret' was to be accessible from the radio cabin. Emerson produced a prototype, but even after favourable reports the project was not proceeded with.

Details of the Grumman (Emerson) Model 150 SE-1 and -2 Mid-upper Turrets.

Aircraft: grumman TBF-1 and -3 Avenger.
Position in aircraft: Mid-upper.
Armament: One 12.7 mm (0.5 in) Browning M2 gun.
Ammunition: 200 round magazine under gun
Field of Fire:
Traverse: 65 degrees either side of aft.
Elevation:75 degrees
Depression: Horizontal.
Gunsights: Navy Mark 9 reflector sight; Mark 11 ring-and-post sight as standby.
Motive power: Amplydine electrical.
Fire control: Magnovox electrical system.
Armour: 1/4 in plate to gunner's front.
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Post by Robert Hurst » 12 Feb 2005 11:54

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The Martin Type 250 CE series Mid-upper Turret.

The Martin 250 upper defence turret was probably the most efficient heavy calibre mid-upper turret design to see service during World War Two. Although the gunner had a more restricted view than in the Nash and Thompson FN50, the sensitive Amplydine power system and small profile made it a popular choice with aircraft manufacturers. if the war had lasted a further year, in all probability the Martin 250 wturret would have replaced the rifle-calibre mid-upper turrets on the Halifaxes of RAF Bomber Command. Experimental installations had already been air tested on these aircraft, and the Martin 250 CE 23 was standard on the Lancaster B.Mk.VII.

The Martin mid-upper turret armed the Consolidated B-24 Liberator, Martin Baltimore, Lockheed Ventura and the B-26 Marauder, and was found to be a trouble-free and hard-hitting design. It was designed to rotate through 360 degrees in azimuth, and to elevate the two 12.7 mm (0.5 in) Browning M2 guns from -6 1/2 degrees to +85 degrees. The normal speed of rotation and elevation was 15 degrees/sec, while high-speed operation was elevation - 45 degrees/sec, and 30 degrees/sec in rotation.

Power was provided at varying rates from an electrical Amplydine system, giving constant speed in elevation and depression under different loads. The elevation and depression under different loads. The elevation and rotation motors were connected by geared drive units to the gun elevation quadrant and fixed rack rotation system. Clutches enabled the drive to be disconnected so that the turret could be operated manually.

The control handles, which had safety-grip switches, actuated potentiometers which controlled the speed of the elevation and rotation motors. A horizontal twisting movement elevated the gun cradle, and a bicycle steering movement turned the turret. At the top of the right handle was the small red 'high-speed' button.

The main gun controls were in a box mounted over the handles. These were the sight-brightness rheostat, a gun firing isolating switch protected by a red safety cover, gun selector switch, camera switch, a control reset, and booster motor reset.

On the right side of the gunner's seat was the master switch. Before this was closed the two power clutches were engaged. The gun selctor switch was then switched to 'both guns' - in this position both guns fired when either trigger was pulled. The 'individual guns' position was used only when one gun was out of action, each trigger then controlling the gun on its own side.

The sight rheostat dial was then adjusted to suit the light conditions, and finally the control handles were grasped, closing the master switches, and the turret was ready. Under the left thumb was a small red push-to-talk button. The guns were charged by pulling cross-armed on the charging handles beside the gunner's shoulders. On the right arm rest was a demand-type oxygen regulator, the oxygen flow and pressure gauge being usually at shoulder level. The oxygen supply in B-24 turrets was contained in two bottles bolted to the bottom of the seat, but B-26 Marauder turrets used oxygen from the main aircraft supply.
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Post by Robert Hurst » 14 Feb 2005 12:11

Hi

The Martin 250 CE series Mid-upper Turret Cont'd

The heated-suit plug was above the left arm rest, the trouble light being at the back of the right arm rest. If a gun camera was used it was fitted just to the left of the sight. A trigger switch in the right handle crank fired both guns in an emergency. Some models had a foot firing pedal mounted on the left side of the foot rest.

The gunsight was either an N-6A reflector or N-8 retiflector which was mounted in a box-like frame on the sight cradle. The sight could be adjusted for harmonisation with the guns.

The Martin carried four ammunition cans holding 200 rounds each, the cans sliding in on a semi-circular track beneath the guns. These were pushed in until automatic latches locked into place, and the ammunition belts were then fed over the booster unit sprockets down a chute into the gun feedways. For ease of loading, 35-round belts were used to fix on to the main belts and thread up into the guns.

Even though the ammunition cans were directly under the guns, and the guns were fitted with double driving springs, the feeds were not powerful enough to pull up the heavy belts. Two powered sprockets were fitted to a hinged feedway, so that when the pull of the belts exceeded 2.2 kg (5 lb) the feedway tilted and switched on the electric motor of the booster unit.

The profile interrupter protected the airframe. It consisted of a cam enclosed in a protective covering, which was turned by a pinion meshing with the turret ring gear. As the turret revolved, the cam turned at the same rate. On the cam, an exact miniature of the portions of the airframe were engraved. Fitted to the cam cover was a switch box containing three micro switches, and the contact was opened when a micro switch arm struck the engraved part of the cam. This broke the gun firing circuit and automatically stopped the guns firing.

The guns could be adjusted for harmonisation, and the Amplydine unit could be varied for speed by lockable screw heads.


The gunner was protected by a 12.7 mm (0.5 in) thick armoured apron to his front which gave him more protection from enemy fire than any other crew member. This was fortunate, as the turret was not easy to evacuate, and a wounded gunner in a damaged aircraft was in a rather precarious position.

The turret could be manually operated by hand cranks fitted below and behind the control handles. The right crank turned the turret and on the handle was a trigger which fired both guns. The model fitted to the Baltimore also featured a foot-operated trigger switch. Before changing to hand control the power clutches were released, and when resuming powered control care had to be taken to disengage the hand control system. Failure to do this could result in the turret swinging round quickly, which could break the gunner's leg.

The turret could operate successfully up to an acceleration of 3G, and was capable of surviving an 8G acceleration ( in a crash landing, for example).

Details of the Martin 250 CE Mid-upper Turret series

Aircraft and Model:
250 CE 3 and CE 3A.5: Consolidated B-24 Liberator
250 CE 4: Martin B-26 Marauder, Short Seaford
250 CE 7: Lockheed PV-1 Ventura and PV-2 Harpoon
250 CE 8: Martin Baltimore
250 CE 23: Avro Lancaster B.Mk.VII
Position in aircraft: Mid-upper
Armament: Two 12.7 mm (0.5 in) Browning M2 guns
Ammunition: Two 200-round cans per gun
Gunsights: N-6A reflector sight; or N-8 retiflector sight
Field of fire:
Traverse: 360 degrees
Elevation: 85 degrees
Depression: 6 1/2 degrees.
Motive power: Amplydine electrical
Fire control: Electrical Magnovox solenoid units.
Gunfire restrictors: Limit strips preventing mechanical damage. profile cut-off system firing circuit.
Operating speeds:
Elevation: Normal 15 degrees/sec; high speed 30 degrees/sec
Traverse: 45 degrees/sec high speed.
Weight of turret:
Weight of turret and ammuntion:
Armour: 12.7 mm (0.5 in) thick apron to gunner's front.
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Post by Robert Hurst » 15 Feb 2005 12:51

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The Sperry Model A-1 Mid-upper Turret

During the Second World War Boeing Flying Fortress Mks. II, IIA and III (B-17E, F and G) aircraft were operated by a number of RAF Coastal Command sqds as maritime patrol and weather recconnaissance aircraft, as well as being operated by by Nos.214 and 223 Sqds of No.100 Group, RAF Bomber Command as radio warfare aircraft. These famous bombers were fitted with Sperry turrets armed with twin 12.7 mm (0.5 in) Browning guns.

In 1940 the US Army Air Corps had been confering with the Sperry Gyroscope Company, as well as other manufacturers concerning the design of turrets for bombers. it was known that several British companies had developed enclosed power-operated turrets for the RAF, and the facility at Wright Field had acquired some Boulton Paul and Nash and Thompson turrets from Britain for appraisal. These turrets were studied by the engineers of the companies nominated to submit designs for the Air Corps, and were used as the basis of the first design.

Sperry designers, in association with Steel Products Engineering of Sprigfield, Ohio, designed a turret mounting two 12.7 mm (0.5 in) Browning guns. The Sperry K-2 automatic computing gunsight was also modified for use in turrets, and in the summer of 1940 the company received a contract covering the purchase of 540 local control mid-upper turrets and 113 lower remote-control turrets to be fitted with automatic computing sights. The Steel Products Company were brought in as sub-contractors to manufacture the turrets, and the prototype mid-upper turret design was delivered to the Boeing plant at Seattle. It was installed in a B-17C Flying Fortress in November 1940 for flight and firing tests.

On 22nd August, 1941 a conference was held at Wright Field at which Sperry representatives requested to be relieved of responsibility for turret production to concentrate on new turret designs.

The mid-upper turret and under-defence ball turrets were adopted as standard for the Boeing B-17E Flying Fortress, but the lower remote turret was not accepted for service use. It was found that in common with the Bendix and British remotely controlled under defence turrets, visibility through the periscopic sight was unacceptable, for an attacking fighter could not be tracked in the few seconds of the firing pass.
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Post by Robert Hurst » 15 Feb 2005 13:17

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The Sperry Model A-1 Mid-upper Turret Cont'd.

The Sperry Model A-1 mid-upper turret served with distinction on B-17s on many war fronts. It was powered hydraulically by a self-contained electro-hydraulic unit. The gunsight gave the gunner a computed impact point, being developed from the larger K-2 computer-controlled sight, and was known as the Model K-3 (the inverted K-4 was fitted to the ball turret). Visibility was restricted in the first Model A-1s; two metal segments of the cupola to the sides were criticised by gunners, and were replaced by Perspex sections manufactured in the UK for the Eighth AAF in Europe. This modification was soon adopted on the production line.

The gunner could enter the turret from the pilot's cabin or, as was usually the case on an operation, over the bomb bay, when he had to crawl between two columns, turn round, and then rise from a stooped position to stand in the turret. The footrests were adjusted so that the gunner's eyes were behind the optical head of the sight. There was also a sling-type seat which he could clip under him. He then engaged the rotation and elevation clutches, using small crank handles above the ammunition cans. The main circuit-breaker near his left shoulder was switched on, and the sight rheostat adjusted for brightness. In front of the control handles were the ammunition booster motor switches, which were closed.

The twin handle controller was operated in the normal way, with the exception that the right handle incorporated a twist grip which adjusted the sight reticles to the size of an attacking fighter. On the left handle was a safety lever which ensured the turret could not move unless the gunner was in position. Triggers were mounted under the index fingers and a press-to-talk button controlled by the left thumb. A simple method of cocking the guns was by means of two handles suspended from pulleys in the roof of the cupola, which pulled back the charging handles of the guns.

Oxygen was supplied from a demand-type regulator under the control unit, below which was the heated-suit plug. The interphone jacks for the gunner's headphones and throat microphones were situated in a junction box near his left shoulder. A trouble light and switch were mounted in a small box forward of the oxygen, and a Fairchild gun camera could be mounted on the left side of the sight cradle.

The twin 12.7 mm (0.5 in) Browning M2 guns were fed from 125-round ammuntion cans which were loaded from the front of the turret, they were loaded with the rounds pointed to the outside of the turret, pushed forward on to rollers and clipped into position. using two 25-round lengths of ammuntionas feed strips the rounds were fed into the gun feedway and over the booster-unit sprockets. The single link of the feed strip belt was then fixed on to the double link of the leading belt link in the can, using a single round to join them. Each gun was fed from three 125-round cans which were linked together giving a continouous 375-round belt. The cans could be reloaded during a lull in firing. Fastened to the gun's ejection chute were canvas bags to collect the spent rounds.

The Sperry K-3 computer gunsight gave a computed impact point. Information fed into the sight was (1) rate and direction of rotation, (2) angle and direction of elevation, and (3) range given by the gunner adjusting the illuminated sighting graticules and position of aircraft-type indicator set by gunner on the sight body.

The Sperry A-1 was a very efficient turret which, with an experienced gunner able to track smoothly and use the sight to advantage, posed a threat to any attacking fighter.

Details of the Sperry Model A-1 Mid-upper Turret.

Aircraft Type: Boeing Flying Fortress Mks. II, IIA, and III (B-17E, F and G)
Position in aircraft: Mid-upper
Armament: Two 12.7 mm (0.5 in) Browning M2 guns
Ammunition: Three 125-round rechargeable cans
Gunsights: Sperry K-3 computing sight, also fitted with ring-and-bead as standby.
Gunfire interrupter: Limit stops preventing mechanical damage, fire cut-off system preventing fire damage to airframe.
Field of fire:
Traverse: 360 degrees
Elevation: 0 degrees to 85 degrees
Depression: n/a
Motive power: Electro hydraulic unit.
Fire control: Electrical solenoid units.
Turret speed: 40 degrees/sec.
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