Underwater Security addresses the protection of land facilities and valuable assets that are vulnerable to attack from the waterside. Attacks may take the form of armed combat divers or the use of
explosives against target vessels or facilities. A complete Underwater Security program also includes examining ships for contraband containers fixed to the hull.
Techniques commonly used are underwater video cameras and acoustics (sonar). In most harbors underwater vision is extremely limited. Sonar, however, is not restricted by optical conditions and can
be used to sweep or "clear" areas to ensure they are clear of foreign objects such as mines, Underwater Improvised Explosive Device (UIED), or contraband.