The submarine was infested with numerous independent internal communications circuits, consisting of wiring and special phone jacks. To use them you simply plugged in a sound-powered handset or headset, and spoke. Or you just listened, if you were Seaman or below in rank. For example, one circuit simply connected the conning tower to the sonar shack. Another circuit connected the bridge, the conning tower, and the maneuvering room. Another connected the bridge, the conning tower, and the radio room. Another connected the bridge, the conning tower, the wardroom, and the skipper's stateroom. There were lots more. They all worked without external power or batteries, and I was always amazed at how well they functioned. It was a technology from the turn of the century, but it even worked for the torpedoman, standing watch in a quiet torpedo room in which a dozen sailors were asleep, to communicate both ways with an engineman standing watch between two roaring diesel engines.
It was definitely lo-fidelity, though.
One day the exec decided to run an unscheduled drill. He set it up with the chief torpedoman ahead of time, just the two of them. They figured out a circuit that no one would be using. The exec came to the bridge, supposedly just to get some fresh air. I was the Officer of the Deck, and we were trying to get our act together, since we had just surfaced after a prolonged dive. The exec had to tell me about the drill, since he did not know where all the different circuit jacks were. I showed him what he wanted, and he plugged in a handset and spoke to the chief torpedoman.
The exec then turned to me and said, "I think I just spotted an underwater reef, dead ahead, close aboard."
All drills started this way, so I was not concerned. I shouted, "All back emergency, left hard rudder." Then I announced over the shipwide announcing system, "Now, collision is imminent forward." I grabbed the handle and I sounded the collision alarm. Just then, the exec spoke to the chief torpedoman over the sound-powered phone, and the boat almost jumped out from under me. For an instant, I thought we really had hit a reef.
For the rest of the crew, the drill was quite realistic, and they all thought we had hit something. I was able to look at the exec and tell from his laugh that he was having fun. He had gone to the forward torpedo room earlier that day, and had come up with a pretext to remove all the torpedoes from the tubes. After we surfaced, he had told the chief to surreptitiously open the muzzle doors to all the empty torpedo tubes. When the drill started, the chief had fired all the tubes simultaneously, causing the boat to lurch dramatically backwards.
When we reviewed the action afterward, we found that the crew had reacted to the "real" collision better than they usually reacted to known drills. That made sense to me. The only permanent damage that had been done was to the Quartermaster's Notebook, which contains the official log of the ship's activities. The signalman of the watch had written everything down, in ink, in an extremely shaky hand. Some kindergartners have better handwriting than that. I got a good laugh when I got off watch and countersigned the QM's notebook entries for the watch.
The crew had been so efficient in pulling out fire extinguishers, life jackets, emergency tools, emergency rations, smoke masks, first aid kits, and other emergency gear, that it took two hours to properly restow what they had pulled out in five minutes.