Australian Cruiser Tank Mk 1 - Sentinel


Speed 48 km/h
Weight 28 tonnes
Crew 5
Country Australia
Armament 1 x 2Pdr Gun (40mm)

2 x Vickers .303 in MG

Armour 65 mm

At the outset of WWIl, Australia's Armoured resources amounted to 4 Vickers Medium Tanks of 1928 vintage, 10 Vickers Light Tanks MKVlA, and 18 locally produced Armoured Cars of three marks. The local production of Machine Gun Carriers was just about to commence at the Victorian Railway Workshops.

When War was declared, Australia's defence needs were analysed, and it was decided in June 1940 that 859 Tanks would be required, of which 340 were to equip one Armoured Division. The remainder being for Corps Troops and 12 months reserve stock. As the British Army had just lost much of its equipment, including Tanks, in France, and the invasion of the UK seemed imminent, it was obvious that Armoured Vehicles would not be obtained from British sources. The US Lend Lease programme had not yet begun, and so Australia would have to supply its own needs.

A Committee was formed in August 1940, to liaise between the Army and the Ordnance Production Directorate to coordinate design and production. Although various designs were examined, a vehicle with a weight of 22 tons was finally settled upon.

The design staff were assisted by Colonel W D Watson, a British Tank expert. He guided the design team and combined the best of British AFV design and current combat experience, with the US ideas designed for ease of production and maintenance. Their final design was known as the Australian Cruiser Tank Mark 1, sometimes known as the Sentinel.


The major innovation was to cast the Tank hull in one piece. This was decided upon as the use of rolled armour plate was not possible as this was being used in other areas, and the riveted designs were not acceptable as when struck by a projectile, the rivets had the tendency to break and fly around the interior of the vehicle.

The automotive design of the Tank was interesting, although relatively simple. It had been assumed from the beginning of the project that an American diesel engine would be used, but these were all required for US production. The standard Cadilliac car engine was available, and 3 of these were mounted in a clover leaf configuration, driving through a transfer gearbox to a five speed crash gearbox. The main gearbox was a modification of the US M3 Medium Tank gearbox, without synchromesh to enable local production. Suspension was similar to the US Medium series, and similar sized bogie wheels and M3 tracks and sprockets were used.

The cast Turret mounted a British 2 pounder Gun with a Vickers .303 inch MG in a co-axial mount. Another Vickers .303 inch MG was mounted in a large cast mounting between the driver and hull gunner.

The NSW Government Railways were chosen to build the vehicle and the first experimental model was completed at the Everleigh Loco Works in Sydney, during January 1942. This was quickly followed by two further experimental types. Extensive testing of these vehicles was conducted first at the Railway's test track at Villawood NSW, and then at the Army's Mechanisation Experimental Establishment at Monegeetta, Victoria. The main faults found were inadequate engine cooling, failure of the rubber bonding of the bogie wheel tyres and the failure of Turret traverse gear when the Tank was on a side slope.

The paucity of the 2pdr Gun had been recognised from the experiences of desert warfare, and so in mid-1942, one of the experimental models was fitted with a 25 pounder Gun in a larger Turret of 64 inches (1625mm) diameter. Firing trials were successful, and it was decided to introduce a 25pdr armed vehicle, designated AC3, and after the 65th 2pdr vehicle. The new AC3 would eliminate the co-driver/hull gunner's position and have a fully sloping glacis plate. The final model was to mount a 17 pounder gun, and this was to be installed after some 400 vehicles were produced.

The first AC1 left the assembly line at the Chullora NSW Workshops in August 1942, and by June 1943 a total of 65 vehicles were completed and delivered. Production was discontinued in July 1943 as Australia's role in land Warfare had switched to jungle Warfare, and an invasion by Japan was now unlikely. Pressure from the US to accept US AFVs and to use the resources of the industry for railway maintenance and the maintenance of the large quantities of US and British vehicles then in the country, contributed to the project's demise.

The vehicle was an outstanding achievement for Australian industry at a time when there was only a very small automotive and defence capability.


The vehicles produced were used in a training role until the end of the War.

This Particular Vehicle

The vehicle on display was restored to running order between 1988 and 1993 by the apprentices of the NSW Technical Training Centre at Chullora. The restoration work was world class and has ensured the preservation of a fine example of the only type of Australian made Tank. It is one of only a handful of its type left anywhere in the World.