AC 1 Sentinel

[Aufklarung]

After seeing the "Bob Semple" tank in the WW2 quiz thread, I did some hunting around for other Aussie Tanks and found this:

Australian AC 1 Sentinel

Soon after the outbreak of the Second World War it was foreseen that Australia would have to rely on her own resources rather than on supplies from Britain. On the first mention of a tank being built in Australia, there was a great deal of disbelief, as Australia had never developed a tank before and so had no experiance to work with. The lack of expertise in this regard was made up by the loan of Colonel W.D.Watson a senior member of the Mechanisation Board from Britain.
The urgency of this program was increased with the collapse of France and the evacuation from Dunkirk. In November 1940 the General Staff issued the specification of the tank. One weighing between 16 and 20 tons, mounting a 2 pdr gun with 1 or 2 machine-guns. A speed of 30 m.p.h. and a armour thickness 50 mm.
The design that emerged as the Australian Cruiser Mark 1 (AC1), was a blend of American automotive practices with British ideas and a low silhouette. The AC1 used a modified M3 Grant transmission, which was simpler in design so as to be easily produced in Australia. Because of initial problems with this transmission a second prototype known as AC2 was started. This was to use a truck transmission and engines. The draw back to this design was that the weight would have to be kept below 18 tons to give it satisfactory performance. As it would happen this vehicle was never needed as the problems with the AC1 were overcome. The power for this tank would be provided by 3 Cadillac V8 petrol engines which were installed two abreast and the third behind. With, the redesign of the final drive and the bogies, it would be possible to build the tank in Australia. The track was to be the same design as the American M3 medium tanks' T51 track. The problem of rolled armour plate was solved by the use of cast armour similar to that used on French tanks, this may have been influenced by the arrival in Australia of the French engineer, R. Perrier. He had been working in Japan for the French Government but, had left that country in a hurry when the situation in the pacific deteriorated in 1941. The first cast hull was successfully manufactured in October 1941, and the prototype AC1 was complete by January 1942. This was a great achievement for Australian industry as nothing this complex had been built there before. Three prototypes were built being named E1, E2, and E3. After trials some modifications were made to the prototypes and production began. The first vehicles rolled of Chullora tank assembly Shops, New South Wales, in August 1942. The Chullora Shops had been built especially to produce these tanks and had been designed using the American tank arsenals as a guide. They were managed by, New South Wales State Railways. A second tank assembly plant was being built at the same time at Geelong, Victoria and was to be managed by Ford motor Co (Australia) and would have been used to build the AC1 had production not been cancelled. The development vehicles were known as the "E" series of which there were three vehicles. These vehicles were used as test beds for all the development work. A total of 66 AC 1's were built before orders were cancelled in July 1943. They were numbered in the range 8001 to 8065. This was due to the changing situation were America was able to supply all vehicles to equip the 1st Australia armoured Division. The AC1s were used for training and never saw combat. This is a shame as I am sure that had even one went to troop trials in the desert then there would have been a lot more interest shown in this tank.

http://www.thunderandsteel.co.uk/sentinel.html

One of the few Commonwealth tanks of the period that were able to "up-gun" from the 2-pounder gun with little trouble. Shame it wasn't able to be fielded somewhere with Aussie forces. Seems a lot like the efforts that resulted in the Canadian Ram Tanks. The 3x V8 engine configuration must have been quite the site!!

More info at these links:
http://www.angelfire.com/ab5/WWTanks/Au ... tinel.html
http://www.austehc.unimelb.edu.au/tia/913.html
http://users.swing.be/tanks.tanks/complet/653.html
http://www.jed.simonides.org/tanks/sier ... l#variants

regards
A

[adrian]

Of the total 66 Sentinel's built, there is as AFAIK, but 4 left in existence. 1 is held at the Royal Australian Armoured Corps museum at Puckapunyal,Victoria. 1 is at Bovington,1 is in a private collection in the US from what I hear and 1 is being used pulling stumps in western Queensland!

The one at the RAAC museum is a goer, being driven on special occasions (Cambrai Day etc) only.

As a bit of a postscript,when trials for the 17Pdr armed AC3 Sentinel were being held there was a shortage of actual 17pdrs within Australia. The solution was to mount twin 25pdr guns in the turret to simulate the recoil of the high velocity 17pdr! Now that would have been a beast to behold!

adrian

[Coldsteel]

Of the total 66 Sentinel's built, there is as AFAIK, but 4 left in existence. 1 is held at the Royal Australian Armoured Corps museum at Puckapunyal,Victoria. 1 is at Bovington,1 is in a private collection in the US from what I hear and 1 is being used pulling stumps in western Queensland!

The one at the RAAC museum is a goer, being driven on special occasions (Cambrai Day etc) only.

As a bit of a postscript,when trials for the 17Pdr armed AC3 Sentinel were being held there was a shortage of actual 17pdrs within Australia. The solution was to mount twin 25pdr guns in the turret to simulate the recoil of the high velocity 17pdr! Now that would have been a beast to behold!

adrian

I know of around 4 surviving AC1s of the 65 built although my distribution is a little different to yours
AC1 8049 (complete) Bovington tank museum, England
AC1 8030 (restored runner) RAAC tank museum, Victoria
AC1 80?? (lacks external bits like tool bin and trackguards) RAAC TM
AC1 80?? (restored/rebuilt runner, internally incomplete) John Belfield's Melbourne tank museum, Narre Warren, Victoria

There is also the first (and last) completed AC3 "Thunderbolt" serial number 8066 at the Australian War Memorial in Canberra

The vehicle fitted with the twin 25 pdr turret and later the 17 pdr was one of the earlier development vehicles, the E1. The remains of the vehicle are also at the Melbourne tank museum.

The twin 25 would indeed have been impressive, but also impractical!

Coldsteel

[Aufklarung]

Just so we can see what a twin 25pdr armed tank looks like.

SENTINEL AC III [Experimental]

http://www.jed.simonides.org/tanks/sier ... intro.html

regards
A

[Andy H]

Coldsteel wrote:

The twin 25 would indeed have been impressive, but also impractical!

Would this be from a technical viewpoint, a effectiveness angle?

I would agree that on first looks it does look impratical, but what if the vehicle was used just in the mobile artillery role?

Andy H

[D. von Staberg]

Would depend on the turret being large enough to allow the crew to work the guns, endure the recoil and keep up a decent rate of fire.
The Swedish army did a few studies on twin barreled SP Guns and assault guns in the 1950's. None went beyond the paper stage due to crew problems. Recently the concept was reborn when the CV90 IFV got at turret with twin 120mm mortars. The CV90 AMOS is a very usefull beastie indeed. To bad the upcoming defence cuts will probably kill it along with the rest of the armed forces.

[Aufklarung]

Hi
After reading though the links in the initial post, I believe the idea of mounting the twin 25pdrs was merely to test the recoil system and hull for a later mounting of the 17pdr. It was never meant to go into production with 2x 25pdrs. Merely a test bed vehicle in the absence of sufficient 17pdr guns.

Remember the 25pdr was an Artillery piece with short casings, less propellant, and low muzzle velocity. Although 17 is less than 25, it has nothing to do with size of the casing or m/v.

17 pdr firing APC ammo had an m/v of about 885m/sec (APDS=1200m/sec) while 25 pdr firing an HE round only had an m/v of 200-450m/sec depending on the type of HE round used.

One can see now why x2 25pdrs were used to simulate the recoil of x1 17pdr.

regards
A

[Coldsteel]

Would this be from a technical viewpoint, a effectiveness angle?

I would agree that on first looks it does look impratical, but what if the vehicle was used just in the mobile artillery role?

Andy H

The vehicle in question had it turret ring enlarged to 64 inches to see if it could hadle the recoil, and while this would have made the turret less cramped than a production AC3 (which only had a 54 inch turret ring regardless of what anyone else says and I should know I've seen a Mk3 turret sitting on a Mk1 hull and it fits!), having the two 25 pounder breaches side by side would take up a huge amount of room. They would would sweep out a large volume were you can't have any equipment or crew. Remeber also that they are mounted on a shared recoil system so if one fires they both recoil, and you wouldn't want to be loading one when the gunner fires. It is difficult to see how you could fit three men in the turret under these kind of conditions let alone the four you would probably need to have one loader per gun and even if you could to what end? a 25 pounder will only do so much damage and if its not enough reload and fire again. The only real advantage is a much quicker second shot.

If used in a mobile artillery role the rate of fire would be less than a towed 25pdr (I recall reading of one gun crew that was able to fire around 15 shells in one minute) and probably less than the AC3 at 8 rounds in 73 seconds. Maximum elevation of the AC3 is only around 15 degrees and I wouldn't expect any more of the E1 restricting maximum range of the gunns. The AC3 was designed to carry 120 complete rounds although 60 of these were the shorter 20 pound AP shot. It was criticised at the time for only having 7 rounds immediately available in the turret. More were stored in the loaders seat and under the turret basket, some more were stored in a large armoured bin on the left hand side on the gearbox. This isn't too much of a problem for a tank which isn't expected to expend all of its ammo at once, it can stop and mess around with stowage but a mobile artillery piece has to have ammo on hand to keep firing.

The other problem that springs to mind is the close proximity of the muzzles, Battleships that had the guns too close together suffered from blast interference where the muzzle blast of one gun would affect the shell launced form another if fired at the same time reducing accuracy.

So its not so much that you couldn't do it but a question of Why, when an AC3 could already do almost everything a twin 25 armed vehicle could.

Coldsteel

[Andy H]

Thank you Auf & Coldsteel for adding some flesh to the bones so to speak.

Kind Regards

Andy H

[verdenpark]

From the various sources I have read, the production AC3 was only meant to have a single 25pdr. The twin 25pdr was only a test vehicle. The AC4 was armed with the 17pdr. There were four AC1 prototypes built. The last one had the same Christies suspension as a Crusader. It had a fantastic speed, but kept throwing tracks. It was later converted to AC2 standards, with a 6pdr. It was last seen in an underground bunker at the Maribyrnong Ordinance Centre during the 1990's. It is rumoured to have been cut up for scrap when the centre closed.