It was amazing how slow the British were to fully develop the 17pdr as a main gun for armour. Obviously the demand as an AA weapon was a number one priority.
The Australian Cruiser tank (AC1) was a medium tank of sound design which entered production in 1942. Originally armed with a 2pdr, then 6pdr gun which were deemed ineffective by Australian experiences with German armour. the 17pdr gun was mounted. When built this version the AC3 was the most powerful battle tank in the armoury of the Western Allies. The entire project fell aprt due to political interference, military inefficiency and some technical problems.
When designer A. R. Code and Colonel Watson approached the relevent British authorities with their experiences with the AC1 and AC3 developments. From the Australian success of fitting the 17pdr with a suitable recoil system the British were convinced to adapt the 17pdr to their own Shermans. The rest is history.
Source: Armed And Ready-The Industrial development and Defence Of Australia 1900-1945 by A.T. Ross ISBN 0 908031 63 7
Regards Digger.