[88] These are all vitally necessary parts of the defense of the Boston harbor forts. They are only a small part of what would have to be done in case of naval attack. The data used here are not theoretical. They have been developed by actual test.
[89] So developed in sea and land maneuvers undertaken for the purpose of establishing the very points here mentioned.
[90] It is estimated, from careful calculations, that to put out of action a searchlight at night with shipfire at a range of 6,000 yards, more than a thousand shots from 3-inch guns should be required. The fact is mentioned here to illustrate the great strength of harbor defenses against fire from the sea, if there be enough mobile troops on the land to prohibit destruction by landing parties.
[91] That the American harbor defense system and construction are of the very highest type, has been acknowledged many times by the technical experts of the world. More than once the author has heard foreign officers express the belief that they were practically impregnable to naval fire, providing they were fully supplied and equipped with the material necessary for continuous defense.
[92] A generous system of reliefs is imperative in harbor defenses during war. Peace time maneuvers have developed the fact that the mere strain of incessant watchfulness while waiting for an enemy who may appear at unexpected points suddenly, is so great that unless the men have frequent relief, they cannot exert that concentrated energy which is needed instantly in the crisis.
[93] This system of night attack has been developed and tested by actual trial, and is such as is now laid down for battle practice in the tactics of most navies. “The ... squadron will enter ..., and will maneuver at range of about 9,000 yards from Fort ..., firing heavily, to induce the defense to expend as much ammunition as possible.”--Extract from actual orders in author’s possession, given to a squadron of battleships and cruisers for night attack. It will be noted that this distance is less than one-half the range of the 12-inch rifled mortars in a harbor defense battery.
[94] The search-light system, recognized as a vital part of harbor defense by the Endicott Board on harbor defense (appointed in 1885) has grown steadily in importance with the steady increase in ship armament and ship speed. A thoroughly efficient installation of search-lights for modern harbors demands as much scientific calculation and interlocation as do the gun-systems. If the search-lights cannot infallibly find any vessel that may approach within range, the guns of the fortification are useless.