 In addition to the prototype, refinement of the Wellington's design was influenced by the issuing of Specifications B.3/34 and B.1/35, the latter of which had led to the parallel development of a larger bomber aircraft, the Vickers Warwick.According to Andrews, the Wellington was practically redesigned to form the first production model of the aircraft, during which extensive details attributed to the Warwick were added, such as the deepening of the fuselage, the lengthening of the nose, a reshaped horizontal tail unit, and an increased crew complement for four to five members.Other changes made included the adoption of a retractable tailwheel and constant-speed propellers; the Air Ministry also requested the adoption of a Nash & Thompson-design ventral turret in place of the Vickers design.