by researcher Steve Guy
edited from an email message to TANKS!

I have just completed a bit research in to the Sentinel, and survivors that I know of. There turns out to be more than I first thought , including a rare AC3 .

History of the Australian Cruiser (AC) came about when it was realised that Great Britain would be unable to supply Australia with tanks due to fill her own requirements ,after the fall of France and the evacuation of the B.E.F. The Australian government asked if Britain would send an advisor to help with the development of Australia's first tank. To which Britain sent Colonel Watson in December 1940.

Colonel Watson set off for Australia via the U.S. were he spent some time checking out the latest developments in Armoured design and production, Watson decided that the design of the M3 gear box and final drive was just what he needed for the Sentinel.

In early 1941 a wooden mock up of the AC1 was built it was to incorporate many of the lessons learned though experiences in the war up that point.rolled steel and cast armour was to be used through out its construction. Utilising only alloys obtainable in Australia.

Due to problems with the manufacture of the gear box it was decided to try and build the Sentinel with as many Commercial mechanical components as possible, therefor in July 1941 the AC II project was started.The limitations of using truck engine sand drives soon became evident however and so in September 1941 the AC II was abandoned.

By this time the problems with the manufacture of the AC I gear box had been solved and the first cast hull had been completed in October 1941 which was a great achievement as nothing this complicated had been attempted by Australian industry before. The first AC I was complete in January 1942 and trailed the results were then used to incorporate various modifications to the production models which began to roll off the assembly lines at Chullona Tank assembly Shops ,New South Wales in August 1942.

A total of 66 AC I were built when production ceased as the tank supply problems had been solved by the Allied nations by this time.

The AC I was ahead of it'sBritish counter parts in that it was designed to be able to be up gunned from the 2 pounder to the 6 pounder when it became available how ever this gun was needed in the middle east so none were allotted to the AC I project. So in order to give the tank a bigger punch the 25 pounder was tested in the AC I at Williamstown Victoria .

The 25 pounder was intended to be placed in the improved Sentinel to be given the title AC III which also incorporated a smooth glassis plate dispensing with the hull mounted machine gun and gunner.

By this time the 17 pounder was being produced in Australia and tests were conducted to see if it was practical in mount it in the Sentinel. Two 25 pounder guns were mounted side by side in a modified turret to see if it was able with stand the recoil effects of the 17 pounder as the recoil of the twin 25 pounders was estimated to be 20% more than that of the 17 pounder.It has been stated that these guns were fired using a lanyard at a safe distance from the vehicle. At least one Sentinel was equipped with the 17 pounder when all production was stopped.