In regards to submarines, part of the reason is the way the patrols are conducted:
- Traditionally, submarine patrols are secret. That means that only the captain and say, a few other officers know the exact route and location of the submarine on a given day. Rather, the shore base just gives the submarine a general route to take while on the patrol, and most of the crew is then only given general updates as to their position while the patrol is underway.
- Likewise, communication between the submarine and the shore base is always kept to a minimum to keep the submarine's location a secret by preventing the radio calls from being triangulated. A submarine can go days with out checking in radio wise. When it does check in, the calls are very short.
As a result, the shore base can learn that the submarine is missing several days late- and then not know exactly where it went missing from.
Then factor in that submarines are designed to say hidden. They are designed to be stealthy shape wise and are coated with special material that absorbs sonar waves. This keeps them from being easily found by both enemies and when needed, rescuers.
Thanks for the compliment. Submarines were one of my reading interests for years.
In regards to the crush depth, like many aspects of submarines, the true crush depths are secret. Rather, only a normal deep operating depth is published. Say, 1500 feet.
