American Fixed and Free-Mounted Gunsights used by the RAF

[Robert Hurst]

Hi

American Reflector Sights

In 1931 the German Oigee company produced a reflector sight, the ENI (Electrische Nivellier Instrument, or Electrical Levelling Instrument). Germany was forbidden to produce armaments at this time, so the company used this acronym to promote sales. Lt. Col. Jacob West, the US Air Attache, sent an example to McCook Field, where it was tested on Boeing P-12F aircraft by the 17th Pursuit Group. As a result, the Armament Laboratory at Wright Field designed an American version, an L-shaped housing in which a central cross graticule was surrounded by eight small arrows to assist sighting. This was the forerunner of the American 'N' series used by the US forces for the next 20 years.

The US Army Air Corps introduced the N-series sights developed by Ernest Baldridge, of the Armament Laboratory at Wright Field. The N-1 was tested on the XP-6H, and then by the 8th Pursuit Group in January 1933. These trials led to the adoption in 1936 of the N-2, which familiarised American pilots with reflector sights. The next model, the N-3, was used on American fighters during the early part of the war.

In 1941 the US Navy adopted the British GM2, designated the Navy Mk 8. It was decided not to use the stadiametric range base system, the graticule consisting of a ring and centre dot. Licence agreements were signed with Bausch & Lomb and Bell & Howell for production in the USA. The British Mk II* was also used in P-51 Mustang aircraft of the USAAF.

When the USA entered the Second World War, the sights used in their turrets were all of US design and manufacture, but several British fixed gunsights were later adopted for the USAAF. The following designs were used by the RAF in Lend-Lease aircraft.

Number: N-2
Type: Reflector
AM Ref: N/A
Comments: Used on A-14, A-18, BC-1, P-26, P-35 & P-47B

Number: N-3A
Type: Reflector
AM Ref: 108B/12
Comments; Used on P-38, Martin & Emerson turrets, P-47C & D

Number: N-3B
Type: Reflector
AM Ref: 108B/68
Comments: Used on P-51B & C

Number: N-6, 6A:
Type: Reflector:
AM Ref: 108B/19
Comments: Most widely used turret sight, with single-ring graticule 35 mm (1.37 in) radius

Number: N-8, 8A
Type: Retiflector
AM Ref: 108/24
Comments: B-17 and B-24 used retiflector principle, where the graticule was projected onto an upper mirror and down to the reflector screen.

Number: N-9
Type: Reflector
AM Ref: N/A
Comments: Some P-51Ds.

Number: L-8
Type:
AM Ref:
Comments: Spirit level on sight head.

Number: L-3
Type: Reflector
AM Ref: N/A
Comments: Made to fit late P-38 cockpits.

Number: Navy Mk 8
Type: Reflector
AM Ref: 108B/20
Comments: British Mk II without stadiametric ranging, used on P-47, Avenger and some P-51s.

Number: Navy Mk 9
Type: Reflector
AM Ref: 108B/21
Comments: Based on British Mk IIIA

Caption to centre drawing: The N-6 reflector sight used on US turrets.

Caption to bottom drawing: The American N-8A used the retiflector system, in which the graticule was projected up onto a Mangin mirror at the top of the sight body, from where it was reflected onto the semi-reflective reflector screen.

The above text and photos were taken from "British Aircraft Armament Vol.2: Guns and Gunsights", by R Wallace Clarke.

Regards

Bob

[Robert Hurst]

Hi

American Computing Sights

Coastal Command and some special-duty squadrons used Boeing Fortress IIs/IIIs (B-17F/G) and Consolidated Liberator IIIs (B-24E), whose turrets used Sperry sights, which gave the gunner a computed impact point allowing for deflection. These were mechanical rather than gyro-controlled, but effective. The K-3 was used in the Sperry dorsal turret of the Fortresses. The Sperry ball turret used the K-4, in which the sight head was at the bottom of the housing. The K-3 was too large for the Martin dorsal turret of the Liberator, so the K-9 was developed in which sighting head was remote from the computing unit.

Caption for top photo: The American K-4 computing sight used on Sperry ball turrets. This was the 'upside down' version of the K-3 used on mid-upper turrets. View through the K-3. The ring and bead was the standby sight.

Caption for centre photo: The Sperry K-9 turret sight in which the computer was remote from the sight head.

Caption for bottom photo. US K-13 sight used on waist guns on some Fortresses and Liberators.

The above text and photos were taken from "British Aircraft Armament Vol.2: Guns and Gunsights", by R Wallace Clarke.

Regards

Bob

[Robert Hurst]

Hi

American Ring and Bead Sights.

The flexible guns fitted to some US aircraft operated by the RAF were aligned by an assortment of ring and bead, or 'iron' sights, as the Americans called them. They were designed to use 35 mm (1.37 in) radius rings in two ways: the sight base system, where the eye to ring distance was fixed, or the fixed base method, in which the distance between the ring and bead was fixed.

[Robert Hurst]

Hi

The Boeing B-29 Washington Remote Control Sighting System.

Although these aircraft were only supplied to the RAF in the 1950s, I thought that it would be of some interest to include something about the sighting system of these advanced aircraft.

These advanced bombers were fitted with remote turrets controlled by five sighting stations. Each station contained a controller which incorporated a reflector-type sight linked with a computer and four Selsyn signal generators. As the gunner tracked a target, the Selsyns transmitted information to receivers in the turret which controlled servo motors on the gun control system. When the gunner acquired the target, he set the aircraft type on a dial and adjusted a ring of spots on his reflector screen to correspond to the target's size, which gave the computer the range. As he tracked the target, the computer analysed the rate of movement which enabled it to predict the lead angle. The Selsyn signals were processed through the computer, which adjusted the signals so that the guns pointed to a position in space where the target would be hit.

This system, known as the Remote Control Turret System (RCI), was produced by the General Electric Co. It needed to be very accurately harmonised and set up, and gunner's required a five months' training course to become operational.

Caption to top photo: A gunner using the pedestal sight of a B-29 Washington. Signals from these remote sighting stations were relayed to the computing system which controlled the guns and made the correct allowance for deflection, range and 'own speed'.

The above text and photos were taken from "British Aircraft Armament Vol.2: Guns and Gunsights", by R Wallace Clarke.

Regards

Bob