The M113 was the result of a mid-1950's US requirement for a lightweight, armoured infantry vehicle. The Fire Support version arose from experience during the Vietnam war and the need to improve the firepower of the M113. A number of different turrets were tried and it was the Australians that opted for the turret from the obsolete Saladin armoured car which was fitted to 18 M113. This variant was eventually adopted as the M113 Fire Support Version.