Complex sentence: The drawbridge had been jammed in the down position by a German shell and had not been repaired, the (wall bunkers) with Hotchkiss revolver-cannons protecting the moats were unmanned and over of explosive charges had been placed in the fort to demolish it.
Split into simpler sentences: The drawbridge had been jammed in the down position by a German shell and had not been repaired. The (wall bunkers) with Hotchkiss revolver-cannons protecting the moats were unmanned, and over of explosive charges had been placed in the fort to demolish it.