Coast artillery

Coastal artillery is the branch of the armed forces concerned with operating anti-ship artillery or fixed gun batteries in coastal fortifications.

From the Middle Ages until World War II, coastal artillery and naval artillery in the form of cannon were highly important to military affairs and generally represented the areas of highest technology and capital cost among materiel. The advent of 20th-century technologies, especially military aviation, naval aviation, jet aircraft, and guided missiles, reduced the primacy of cannon, battleships, and coastal artillery. In countries where coastal artillery has not been disbanded, these forces have acquired amphibious capabilities. In littoral warfare, mobile coastal artillery armed with surface-to-surface missiles still can be used to deny the use of sea lanes.

It was long held as a rule of thumb that one shore-based gun equaled three naval guns of the same caliber, due to the steadiness of the coastal gun which allowed for significantly higher accuracy than their sea-mounted counterparts. Land-based guns also benefited in most cases from the additional protection of walls or earth mounds. The range of gun powder based coastal artillery also has a derivative role in international law & diplomacy wherein a country's three mile limit of 'coastal waters' is recognized as under the nation or state's laws.

...
Wikipedia