*see the comments on the ww1 and ww2 tanks * Sturmtiger sent me these after his visit. He asked me to post these, so here they are!
It's an M52A1.The 'M' designation means the vehicle was tested and adopted by the US Army.It looks to me as if the hull is based on the M41 Walker Bulldog.
I'd like to know what the XM551 (the last pic) is all about.It's obviously based on the M551 Sheridan.It looks like a Sheridan on steroids with a ramp attached to the front.
Hmm... the turret is most definitely that of the Sheridan. I'm guessing a pre-production model (as 'X[insert designation]' usually implies).
This site refers to the ramp as the bow surfboard, which with the inclusion of other attachable surfboards allowed the M551 to float.