Well it you insist The Austrlian Cruisers began with a General Staff specification issued in November 1940 after it became clear that modern tanks would not be forth comming from Australia's traditional supplier of military hardware, Great Britain. After obtaining an AFV design expert from Britain and sending one engineer to the United States the concept for the design settled on an Australian built variant of the US M3 Medium tank. The Australian Cruiser (AC1) would use the lower hull, engine, transmission, final drives, tracks, and suspension of the M3, mated to an upper hull and turret designed along the lines of a British cruiser tank. A Mk1 Crusader was obtained from Britain to assist with the project. The specification had by this time morphed into more of a heavy cruiser or medium tank design than the true high-speed cruiser tank. Design work started in earnest during 1941 and the project began to run into trouble with the limitations created by the lack of suitable heavy industry then available in Australia, including the quantity and thickness of rolled armour plate, machine tools and gear cutting capacity. Trying to side step these limitations the designers got to work on an alternate AC2 design built around imported heavy truck components. This failed miserably when the target weight and armour specification could not be met. Work was then refocused on the original AC1 design. Where necessary changes were made to simplify the M3 components to match the production capability of Australian industry. Suitable nickle-free cast armour was developed by BHP, the firm of Bradford Kendall developed the skills and facilities need to cast the hull, and turret as one piece. Roller bearings and syncromesh gears were eliminated from the M3 gearbox design and final drives. Cadillac V8 automobile engines were adapted to power the tank. In the end the AC1 had very little in common with either the M3 Medium or the Crusader. Powered by the combined output of three V8s driving a heavily modified M3 gearbox and final drive system, the tracks and suspesion wheels were the only interchagable parts with the M3. Armed with a 2 pounder tank gun and two 7.7mm Vickers water cooled machine guns and armour 65mm thick, the 2pdr, Mk19 wireless, and crew layout were the only thing in common with the Crusader. The first 3 hand-built vehicles, the "E series", were available for tests, trials, and to further design work in early 1942, shortly after Japan went to war in the Pacific. Production of component parts began later that year and the first production vehicles appeared in August and were designated "Sentinel". Even before the first production vehicles had been assembled it was known the the 2pdr was insufficient in destructive power with regard to German tanks being encountered by units of the 2nd AIF in North Africa. A variety of alternative armaments were considered ranging from the obsolecent WW1 18pdr field gun to the new 3.7inch anti aircraft gun before settling on the 25 pounder field gun/howitzer. A prototype turret mounting a 25pdr was tested on the second prototype AC1, the E2, and apparently later mounted on the second production vechicle serial number 8002. Firing trials were extremely encouraging and the weapon selected for the improved cruiser tank, the AC3. The AC3 dispensed with the hull mounted MG and gunner to make room for the much larger 25 pounder ammunition. Further room and power was created by bolting the the 3 V8 engines to a common crank case in a similar fashion to the later A57 Chrysler multibank. The 25pdr with a shortened recoil system partly developed from experience gained from the redesign for the 25pdr into the Short 25pdr pack gun, was mounted in a turret slightly larger than the Sentinel's but using the same turret ring. This resulted in a somewhat cramped environment, but still could be used as an effective fighting machine. Only one was completed before the project was terminated. A still more advanced design was on the drawing board, the AC4, with many of the features of the AC3 but with a much larger turret ring and turret able to mount either a 17 or a 25 pounder. Some early tests were carried out on the first of the development vehicles, the E1, using a twin 25 pounder, and later a 17 pounder. The desing was not completed before the project was cancelled. AC1 Sentinel: 1x 2 pounder tank gun, 130 rounds 2x Vickers MG 65mm armour 28 tonnes 3x Cadillac series 75 V8 40mph AC3 1x 25 pounder tank gun, 120 rounds 1x Vickers Mg 65mm armour 30 tonnes 1x Perrier-Cadillac (3x V8) AC4 1x 25 or 17 pounder tank gun, 120 or 65 rounds respectively 1x Vickers MG 65mm armour 31 tonnes
Excellent post Gryle! A great design, and my favourite 'what if' tank. If I may add a few pictures... Sentinel AC 1: (picture from http://www.diggerhistory.info/pages-arm ... museum.htm ) (picture from http://en.wikipedia.org/wiki/AC_Sentinel_(tank) ) AC 4 / E1: (picture from http://en.wikipedia.org/wiki/AC_Sentinel_(tank) )
That would be Puckapunyal's restored one, 8030. Not really sure, 8045? puts it outside the first 25 tanks which the army accepted, they never accepted the rest as it was claimed they were defective. Which I suppose is true to some degree, the engine cooling in particular was very troublesome. Not a Sentinel, not an AC4, Ricky. Only the AC Mk1's recieved an official name. That's the E1 in it final guise as a 17 pounder test rig. Note the large driver's hatch, multiple cast part assembly, and trailing return rollers. The AC4 was to inherit the AC3's basic hull design, slopes straight up from the transmission cover to the top of the hull as a smooth plate, about 2" thick at 24 degrees from horizontal. Nice beasts aren't they?
More bits and pieces Difficult to say how they would have done in Europe or anywhere else. They most likely theatre initially would have been North Africa where the cooling problems could only have gotten worse. If the AC1 had been deployed there it probably would have got a reputation little better than the Crusader. The AC3 wasn't fully tested but didn't have anything like as many problems, and the 25pdr would would have made a mess of most things it was pointed at. The British were interested in getting samples of both the 25 pounder and 17 pounder armed tanks and if they had been supplied and copied to any degree the most likely outcome is probably an AC4-like turret dropped on to an M4 hull in place of than the Firefly, rather than the production of a whole new tank design. Photos of the AC3 (from http://www.mheaust.com.au/Aust/Research/Sentinel/sentinel13.htm) Pictures of the AC3 and AC1 powerplants at http://www.oldcmp.net/triplecaddy.html And what happend to some of them after the war http://www.oldcmp.net/cruiser.html
