They were developed in the 1960s and have been largely superseded by wing and vest type BCs, primarily because the buoyancy is concentrated in front of the diver when full, and behind the neck when partially filled, producing a tendency to shift the diver's center of buoyancy towards the head with inflation, which adversely affects the diver's trim underwater. The ABLJ's location on the diver's chest and round the neck provides the best buoyancy distribution of the buoyancy compensater designs when it comes to floating a distressed, fatigued or unconscious diver face-up on the surface in the event of a problem.