World War II saw the use of semi-recessed bomb bays which, being an uncommon variation of the fully recessed bomb bay, was a design compromise for aircraft that were intended to carry bombs but did not have sufficient fuselage space for a fully recessed bomb bay; such a design did not allow for the inclusion of bomb bay doors.
World War II witnessed the use of partially hidden bomb bays, which were an unusual variation of fully recessed bomb bays. This design choice was a compromise for aircraft designed to carry bombs but lacked sufficient fuselage space for a fully recessed bay; such designs did not accommodate bomb bay doors.