I think you must mean they should have use the tanks to stop the evacuation of Dunkirk, not Dieppe. Dieppe was an outright slaughter of mostly Canadians, when the allies made a test case out of an attempted landing to see what would work for the eventual assault on Fortress Europe.
Quite right. I was keyboarding faster than I was thinking, though both the British Expeditionary Force in France fleeing Dunkirk and the Canadians and Royal Marine Commando force [including 50 accompanying U.S. Army Rangers] of Operation Rutter and Operation Jubilee were both somewhat badly mauled.