Just have a quick question that a cursory Googling didn’t answer. Are the Lee and Grant different variants of the M3, or were both names used to refer to the same tank (e.g., Brits using one name and Americans the other)? Sorry for the basic question, but I would like to get a quick answer so that I don’t lie awake nights pondering this. 
Thanks for any replies.
Dave
The Lee and Grant were variants of the M3 medium tank design. The Lee was the standard US version. The Grant was used by the British, with a larger, redesigned turret.
as hulk said the brits used a different turret the american ver had a small turret on top of the larger one with a mach gun in it
the brit just had the one large turret
British Lee = M3
British Grant = M3 with turret to meet British requirements
The British always used names rather than numbers, for example Sherman, Stuart, Chaffee. Usually named after famous US generals.
Chris
Thanks to all who helped out with this. It’s perfectly obvious now.