Reduction gears are usually shrouded in mystery, at least in the U.S. Navy. They were mostly built by GE and the Navy didn't own them - they were leased from GE. The access ports were locked and only the chief engineer had the keys. I don't recall ever seeing one opened. They are quite complicated with very close tolerances and machining. It was considered an act of sabotage to tamper with them. I remember a gator freighter (LST) at Norfolk where some disgruntled sailor managed to break one of the locks and put a foreign object inside. They pulled the brow up from the pier and essentially arrested the entire crew in the attempt to find the guilty party. It was on the same pier as my ship and we had to walk by. They weren't even allowed on the weather decks and the ship looked deserted, except for the NIS agents (now called NCIS) who were crawling around. It was scary and made an impression. I don't know what the outcome was.