adjective. Directed against enemy submarines.

adjective. Intended for use against submarines.

adjective. defensive against enemy submarines

"The U.S., British and Canadian navies won the Battle of the Atlantic, thanks to their use of convoys and exploitation of advances in antisubmarine warfare technology and tactics—but only after suffering horrendous losses in blood and treasure."

defensive  

submarine  

air-defense  anti-submarine  anti-tank  antiair  antisub