Most all had riveted hulls and when hit, even if not penetrated, the impact knocked the rivets loose so they spanged about inside and killed the crew just as efficiently as if they were machine-gunned. A few later ones had welded hulls.
I found it interesting that they were used up until the end of the war in the China-Burma area as the Japs tanks were so thin-skinned, they weren't a threat. Anti-tank guns were a different matter.