unfortunately it seems to be always the M2 or M3
It's because these were in fact the only models supplied in quantity through the period. The Americans, probably sensibly, valued production over performance and once they had a reasonable design standardised on this and just built more and more of them. They did develop many variants of this design for employment in different roles, but the basic shape is readily recognisable in all of these.
I think you can get away with a shift to the M75 in 1951 as you've indicated. It didn't get into serial production until 1952 but there were enough of them around in 1951 to indicate that it was going to be the next developmental step. Without a timeframe I'm not sure which way you should jump for #7, though. Chronologically the next type introduced was the M59 which started production in 1953 but which, like the M75, was phased out pretty quickly as an inadequate response to the demands made on it in Vietnam. The true qualitative advance came with the M113, but that didn't arrive until 1960.
My suggestion would be to use the M2 for #1 and then successive M3 variants for #2 through #5. That wouldn't be altogether ahistorical since the introduction of these coincided with advances in doctrine on the use of mechanised infantry. In that light they can be seen to represent developments in that type of force. You could certainly broaden your image base by introducing armoured cars into the progression but that might be a little confusing given that they have a category of their own.
When it comes to Commonwealth forces things really get messy. As the war progressed they became increasingly dependent on US production so that 'local' types tended to fall out of service and be replaced by M2s and M3s. I'll do a little digging and see if I can't come up with some sort of sequence for the Brits at least.
Last edited: