Thinner armour or different composition?Never mind adding armour, I vaguely recall hearing somebody describe their run through Europe in a Cromwell and leading his troop in a ditch-hopping escape from some unexpected German chaps who gave him a hot reception.
Apparently, his tank was the quickest out of his squadron and the best jumper. Turned out that his tank was actually a training vehicle with thinner armour. However, as the crew had fought their way through from Normandy into Holland(?) in that tank and seen many of their fellows taken out, they decided to keep their Cromwell Light rather than exchange it for a regular Cromwell.
I think the story-teller might have been Bill Bellamy, but I don't know.
I know that the US used to make mild steel training tanks as late as the M48.