Crash dive

Crash diving from the surface to avoid attack has been largely rendered obsolete with the advent of nuclear-powered submarines, as they normally operate submerged.

On German U-boats of World War II, a crash dive began with the Captain or senior lookouts giving the order "Alarm!"

A few seconds later, the crew would flood the rear ballast tanks to prevent the bow-down angle from lifting the boat's stern out of the water.

On submarines with direct drive, the crew disengages the diesel engines from the propeller shafts and switches to electric motor propulsion.

The crash diving rate of a missile submarine is also not relevant since it can stay submerged for very long periods of time, and is not expected to ever cruise on the surface when in range of enemy units of any type.