depth charge

Short definition from Wiktionary

Noun

1. 1
   A form of bomb, launched from a ship or dropped from an aircraft, that is designed to detonate at a certain depth underwater for the purposes of attacking a submerged enemy, especially a submarine.
2. 2
   Synonym of bomb shot (“type of mixed drink”).

Verb

1. 1
   To attack (a target, usually a submarine) with depth charges.
2. 2
   Alternative form of depth charge.