GMC's huge Twin Six V12 gas engine was made to take on its diesel counterparts, powering fire trucks and farm machines, but it didn't stay on the market long.

Service: US Army, USMC Engine: MTU Detroit Diesel 12.1 liter Variants: M977 cargo truck, M978 tanker, M983 tractor, M984 wrecker, M985 cargo truck Crew: 2 Range: 400 miles Speed: 62 mph The Heavy ...