The Australian Cruiser tank project was an audacious venture for a country with 

limited heavy industrial capacity – and no experience in the design or manufacture of 

a modern cruiser tank. 

The genesis of the project was a technical intelligence report prepared in mid-1939 by 

Major Ronald Hopkins about the strength of the Imperial Japanese Army’s tank force. 

The report was so alarming that the Chief of the General Staff called for the design 

and construction of a light cruiser tank to combat a possible Japanese invasion of the 

Australian mainland. Initial design work was commenced by Army design staff in late 

1939, but with the creation of the Department of Munitions in mid-1940, the 

responsibility for tank manufacture passed to that department. From there, the project 

brought together a consortium of Munitions, Army and private industry which 

together developed the Australian Cruiser tank, with the Mark 1 version called the 

‘Sentinel’. 

It was not without its problems, a project hampered by constant changes in 

specification and fraught with overly optimistic delivery estimates, rivalries that were 

both inter-departmental and personal, questionable management decisions, and a total 

dependence on the supply of vital components from the USA.

Conversely, there was also remarkable innovation and ingenuity. An unconventional 

formula for Nickel-free cast armour and the hull cast as a single piece were worldfirsts, as was the mounting of a 25-pdr main armament, followed soon after by the 

formidable 17-pdr tank gun.

However, by July 1943, with more tanks having arrived from overseas than the Army 

needed, and with little prospect of the delivery of combat-ready tanks from local 

production any time soon, the Australian Government decided in principle to the 

cessation of the Australian tank programme, making the final decision to terminate in 

February 1944. Despite the enormous resources devoted to the project, only 65 AC1 

Sentinel tanks were ever manufactured.