A grappling hook or grapnel is a device that typically has multiple hooks attached to a rope or cable; it is thrown, dropped, sunk, projected, or fastened directly by hand to where at least one hook may catch and hold on to objects. Generally, grappling hooks are used to temporarily secure one end of a rope. They may also be used to dredge for submerged objects.

Naval boarding action is an offensive tactic used in naval warfare to come up against an enemy watercraft and attack by inserting combatants aboard that vessel. The goal of boarding is to invade and overrun the enemy personnel on board in order to capture, sabotage, or destroy the enemy vessel. While boarding attacks were originally carried out by ordinary sailors who are proficient in hand-to-hand combat, larger warships often deploy specially trained and equipped regular troops such as marines and special forces as boarders. Boarding and close-quarters combat had been a primary means to conclude a naval battle since antiquity, until the early modern period when heavy naval artillery gained tactical primacy at sea.