Standard Flying Twenty chassis with ambulance bodywork and canvas top cab. This 20 HP chassis, which was not to be continued after the war, differed from the 14 HP in having a six-cylinder engine of 2664-cc and 9 ft 8 in (v. 9 ft) wheelbase. Bore and stroke were the same as for the four-cylinder 14 HP. namely 73 x 106 mm. As can be seen, the bonnet was slightly longer. The RAF used similar ambulances on the 14 HP chassis for domestic use. Their bodywork and finish, however, were more austere.