The SB401, being a Mark 4 Shorland, was fitted with a V8 engine. In order to accommodate this larger engine the radiator was moved forward, which is the key recognition feature for this model. The other main improvement was the addition an extractor fan in an armoured cowl mounted on the roof. This must have improved crew comfort enormously compared with the SB301 which had little natural ventilation. Various arrangements of smoke dischargers and public address systems were available as extras as they had been for any other Shorland.
