The Fallgrubenabdeckung (cover for drop pit) was produced in only small numbers. It was used in B-Werken built from 1936 and in Hohlgängen and served two purposes. If it was lifted it could be used as gasproof armoured entrance door and if it was sunken it served as a bridge over the 3.5 m deep drop pit. It had a loophole for small guns. Only three survive of which two can be found in the B-Werk of Besseringen.
A 99P9 in sunken position.