Thunder Afloat (1939)

Barely qualifies as a romance film, unless you count an interrupted kiss and shoving your girlfriend in the water romance.

A wrench is used as a weapon.

Navy subchasers launch depth charges over the side as well as through the Y-gun on deck. Nazi submarine uses on-deck cannon and launches underwater torpedos, sinking ships, killing sailors. Submarine commander also uses explosives to blow apart and sink barges and the tug boat towing them, stranding all sailors aboard. They take hostage a sailor and submerge, undergoing depth charge assault.