Vehicles in Fallout
The M2 was developed by John Browning in 1917-18, so that's no problem.I didn't know Hummer & .50 cal was developed in the fifties...
But you're right about the Hummer. So use a Jeep instead. The U.S. Army mounted a machinegun on it in WWII and used it as a scout vehicle (among many other uses). However, I am unsure whether or not the M2 was ever mounted on this vehicle, due to recoil. I believe that the M1919A4 was used, however, as was the M1917* watercooled machinegun. Please note that both of these weapons were designed by John Browning (most of the small arms used in the U.S. Army during WWII were of his design).
*I am unsure whether this is the proper designation for this weapon.
Oh, of course M2 existed back then... How silly of me.
Anyways, I see no problem why there weren't many vehicles stored for the nuclear war. You can't be sure there are oil/gasoline reserves + vehicles take a whollopy lot of space. In my opinion it wouldn't be that much of a surprise if there weren't a bunch of Hummers/Jeeps collecting dust in the corners of the Vaults...
Anyways, I see no problem why there weren't many vehicles stored for the nuclear war. You can't be sure there are oil/gasoline reserves + vehicles take a whollopy lot of space. In my opinion it wouldn't be that much of a surprise if there weren't a bunch of Hummers/Jeeps collecting dust in the corners of the Vaults...