It's the compartment where a B-52's ordnance is carried & from which it's dropped
The 1760 IWBU will allow the B-52 to carry the AGM-158B JASSM-ER 
and the... [DOC] [TLE] Boeing B-47 Stratojet - Wikipedia [PAR] The Boeing B-47 Stratojet (company Model 450) was an American long range, 
six-engine, turbojet-powered strategic bomber designed to fly at high subsonic 
speed and at high altitude to avoid enemy interceptor aircraft.