IDIOMS

crash dive

(idiomatic, military) An emergency maneuver by a submarine in which it suddenly descends, especially to considerable depth, usually in order to escape an attack or to avoid a collision.

Example: 2000 March 19, Charles M. Cooke, "Letters: Loose Lips, Sinking Ships," Washington Post (retrieved 25 Oct 2015):
  As the crash dive began at 1:50 p.m., the overboard ventilation valve had not been closed, which resulted in tons of water flooding the submarine.
A rapid descent by a person or thing ending in a violent collision.
1985 Oct. 4, Mel Gussow, "Theater: Three by Sam Shepard," New York Times (retrieved 25 Oct 2015):
  In "Icarus's Mother," a skywriter salutes two girls on a beach with the message, "E=MC2," and then swirls into a deadly crash dive.