The marine container door locking system, commonly known as the twist lock or cam lock mechanism, secures the double rear doors of shipping containers. It typically consists of vertical steel locking bars, end cam locks, intermediate hinges, and a handle assembly with a lockable latch. To operate, the handle is rotated to move the cams into or out of keeper brackets on the door frame. The system ensures a watertight seal under high stacking loads and rough sea conditions, often featuring a provision for a tamper-evident seal or padlock to protect cargo from unauthorized access.