They were designed in light of problems that more standard tanks experienced during the amphibious Dieppe Raid, so that the new models would be able to overcome the problems of the planned Invasion of Normandy.
De var konstrueret til at tackle en række problemer, som almindelige kampvogne stødte på under slaget ved Dieppe, så de nye modeller kunne overvinde de problemer, der ville opstå under den planlagte invasion af Normandiet.