Whats it like to drive a half track?

I'll pass it on to him. He likes corrections.

In that case tell him I can put him in touch with one of the half track repair/maintenance guys from the 136th Armored Ordnance Bn., so they can compare notes about the M3's top speed. Maybe there was a secret "hop up" technique that he didn't hear about during the war. Although it seems likely an M3 halftrack running down the road at 70 mph would have attracted considerable attention.

To paraphrase an old tanker joke, maybe his "track" could only run 70 mph in reverse. (It's a joke. Do not take this as an attack on your friend.)