page_title: AC4 tank
section_title: History
hierarchical_section_title: AC4 tank / History
caption_attribution_description: English: An Australian developed and built Cruiser Mk III (AC3) tank, fitted with a 17 pounder gun in the turret. (Note: This caption is incorrect, the vehicle shown in the photo is the E1 prototype fitted with a new turret and 17 pounder gun) AWM credit line: Donor S Davies
context_page_description: The AC4 was a cruiser tank designed in Australia in World War II as the intended successor to the AC3 Thunderbolt. Like its predecessors the AC4 was to have a one piece cast hull and turret. The AC4's most important characteristic would be the use of a 17 pounder tank gun.
context_section_description: Reservations about the utility of the 25 pounder in the AC3, and the 25 pounder's limited ability to pierce armour led to experimentation with a 17 pounder mounted on an Australian cruiser.
  A turret was built and mounted on one of the earlier development vehicles to assess the vehicle's ability to mount the foremost Allied anti-tank gun of the day – the British 17 pounder (76 mm, 3 in). This was achieved by mounting two 25 pounder gun-howitzers which when fired together would significantly exceed the recoil of a 17 pounder. In this configuration the tank was tested on 2 November 1942. It fitted with a 17 pounder and after successful gunnery trials on 17 November 1942 the 17 pounder was selected for the AC4 design. For the AC4 the 17 pounder was to be mounted in a new and larger turret, attached by a 70-inch (1778 mm) diameter turret ring, the space for which was accommodated by changes to the upper hull permitted by the compact nature of the "Perrier-Cadillac".
  A design for the tank had been established, however it was subject to a redesign to alter the internal stowage, and include new features not previously considered such as removal of the turret basket, addition of a gyro-stabiliser, and swapping a hydraulic traverse for the electrical system, and torsion bar suspension for the volute spring used up until that point.
  The programme was authorised to build a total of 510 AC4 tanks. The design was not yet finalised when the programme was terminated in July 1943.
caption: AC E1 development vehicle with a test turret and 17 pounder gun
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