The Vickers A1E1 Independent was an inter-war tank designed as a breakthrough tank. With 5 turrets the tank was well armed but it never got taken forward into production, however, the plans were stolen and sold to the Russians (for a grand total of £40) and were said to have inspired the T-35.
for more details see:
https://en.wikipedia.org/wiki/Vickers_A1E1_Independent
Ideal for interwar what-if scenarios.