bulkhead door

A bulkhead door is a heavy, watertight door built into a ship's bulkhead—the internal walls that divide a vessel into compartments.

These doors seal to prevent flooding from spreading between sections if the hull is breached.

The term extends to similar doors in submarines, aircraft, and spacecraft, and to the angled doors covering exterior cellar entrances on older buildings: We carried the furniture down through the bulkhead door.