Three TBM accidents in 1973 and three F7F accidents in 1974 accelerated the CAL FIRE S-2 modification program. As a result, contracts were entered into with four California contractors, Aero Union Corp., Sis-Q Flying Service, TBM Inc. and Hemet Valley Flying Service to modify and tank ten S-2 air tankers during the 1973/1974 winter period. As a result, 12 S-2As were placed in service in 1974 and five more were built by Bay Aviation Services and put into the fleet for the 1975 fire season.