Seacost defense in the 1860s-1910s depended on sea forts protecting harbors, these forts featured "disappearing" guns, large caliber guns on hydrostatic mounts that could elevate them over a parapet for firing, but retracted into armored bays for reloading, giving crews theoretical protection from the enemy fire, like all sea war in the late 1800s the rapidity of technological change caused an evolution in size, weight, power so fast that every aspect of these defenses were usually obsolete before the concrete finished curing.
the main idea of a sea fort was that land based guns could be larger than ship borne guns, and so outrange them, and thus sink ships before they could come in range to fire on the forts, or sink ships in harbor. The problem was that the emplacement plus gun was terribly expensive, goverments built them anyway, but could not afford to keep rebuilding them to keep up with the growth of calibres on battleships, and most penurious governments were loathe to acquiesce in the expenses of target practise with these guns-which could cost 200 us 1889 dollars a shell, so rendering the crews unable to hit a barn when in time of actual war.
...the coming of aircraft and missiles relegated the sea fort to the dustbin by accomplishing the same mission for vastly less expense.