The CHURCHILL tank.
To save reinventing the wheel, here is a very good wiki page about it.
First used at the landing at Dieppe. Not one got off the beach. Germans looked over the Churchills and concluded that the British were getting rid of WW1 kit.
Mounting a 56mm gun, it was obsolete before it really got into combat although its armour was impressive. Made its mark with Hobart's Funnies during D-Day when they were the basis for mine flails, bridging units, AVRE's and flame throwers.
Anoraks enlarged on the funnies here