M. Brindos
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You have the tank marked with Army markings but as far as I know only Marine units has the -A3's. The Army had -A2's A2C's and a few old converted -A1's. The main differences being the addition of the cupola riser and the two extra return rollers on the -A3's. The few converted -A1's had five rollers as well, but the -A2's only had three per side.
Actually most Army M48’s in Vietnam were A3’s. I have been searching photos high and low for A2’s and the only Army unit that I came across with M48A2’s was 1/77 Armor, the Steel Tigers, when they first arrived in county. They later received M48A3’s.
On a side note, all A3’s were rebuilds, not new production vehicles. The last original new production model was the A2. The M48A3 and later M48A5 were rebuilds if earlier versions.
The M48A2 had gasoline engine while the M48A3 was diesel powered.