Pile barrage

Pile barrages, among other names (see § Terminology), are underwater barricades or barrages used for coastal military defence. They are constructed with piles, vertical poles or stakes driven into the bed of a body of water, extending up to, or above, the water line to block the passage of watercraft. They are sometimes also mixed with floating booms and thereof (compare Shoeburyness Boom).

They have been used since prehistory to prevent enemy watercraft from entering waterways or harbors, etc., as to protect the sailing routes to trading posts and settlements.