Australian AC 4 Tank
The AC 4 Cruiser Tank was a development of the AC 1 Sentinel mounting a 17 pound gun instead of the original 6 pounder. To test the feasibility of mounting the 17 pounder, two 25 pounders were fitted to AC E1, a test vehicle. This simulated the forces exerted by the planned new installation. However, the twin guns took up most of the turret interior and had to be fired by a pull string exiting through the turret’s rear.
Following the successful tests, the 17 pound gun was installed. Trials proved successful, but production was not proceeded with, as US and British tanks became available.
Test Vehicle AC E1 With Twin 25 Pound Guns
Two 25 pound howitzers fitted to AC E1 test vehicle 
Two 25 pound howitzers fitted to AC E1 test vehicle
Test Vehicle AC E1 With 17 Pounder Gun
17 pounder gun fitted to AC E1 test vehicle 
17 pounder gun fitted to AC E1 test vehicle 
17 pounder gun fitted to AC E1 test vehicle 
17 pounder gun