The initial main civil uses were as "executive" personnel transports with minimal modifications such as removal of military features, bomb-bay doors sealed shut, passenger-entry stairs in bomb bay, and the conversion of the fuselage to accept six to eight passengers. Improvements developed considerably until the early 1960s, when purpose-built executive types such as the turboprop Gulfstream I became available.Grinsell 1974, p. 44.
