Ac-1 Sentinel:

The Ac-1 Sentinel was an Australian tank type. The producer of the tank was the company New South Wales Railways. The abbreviation Ac means Australian cruiser and marks the type as cruiser tank. In WW2 the threat of Japan increased and Australia needed a possibility to defend itself because Japan showed that they were eager to expand its territory. Another reason to start producing own tanks was that UK was not able to send enough tanks to face the huge threat. The thing is quite special because the hull of the tank was the first to cast in a single piece. It was the only tank to be produced in quantity in Australia. Important is also that no Sentinel tank ever was part in Australian armoured forces because they used mainly British and American tanks when they were again able to establish the supply lines. The development started in November 1940. A problem that occurred was the deficiency of experience in constructing tanks and so the designers got their inspiration from the American M3 tank and the UK provided Colonel W.D. Watson MC who was an experienced tank designer. The Sentinel was inspired by the engine, drive train, lower hull of the American M3 medium tank and by the upper hull and turret of the MK VI. According to the better development of German tanks, the design was changed to be more like an American medium tank, mainly the design was made heavier and the silhouette higher.