How deep can you physically dive?
The maximum depth for recreational diving is 40 metres/130 feet. There is, however, an important caveat: you should always dive within the limits of your training and experience. Open Water Divers* are trained to dive to a maximum depth of 18 metres/60 feet.
First class divers could work 300 ft (91 m) depths while salvage and second class divers were qualified down to 150 ft (46 m).
Can high pressure crush a submarine?
The reason that extreme pressures of the deep can crush submarines is because of pressure differential. The inside of a submarine is held at 1 bar (~14.7psi) for the comfort of the sailors.