Hello Simon:

No big deal......

U.S. Navy fleet boats have two types of propulsion diesels; one is a Fairbanks-Morse
opposed-piston engine and a General Motors vee-type engine. There are two engines in each engine room.

To facilitate engine/generator removal, an access hole is cut through the pressure
hull directly over the engine. The engine is overhauled on the beach, by a navy yard or ship's force.

After the engine/s has been reinstalled, the access plate is welded in place.

Later,

ROBERT M.