[33] With periscopes shot away, a submarine, even though uninjured, is quite helpless. She may escape, if she is in deep water and the assailant is far enough away to give her time to dive and flee, deeply submerged. See loss of U-12 on March 10 merely through destruction of periscope, which permitted enemy destroyers to ram her. [34] Even steam vessels of high power often are rendered helpless by jamming a trailing hawser around the shaft. The revolution of the shaft so macerates and binds the fouled material that the engines are unable to turn the propellor in either direction and only a diver can clear it. [35] The reserve buoyancy of a submarine when awash (technically known as “diving-trim”) is so delicate that 100 additional gallons of water would sink a 300-ton vessel. [36] “From an altitude of 2,000 feet the movements of a submarine torpedo boat may be easily observed unless the water is very muddy”--Capt. V. E. Clark, Aviation Corps, U. S. A., December issue, _Coast Artillery Journal_. [37] Important cities in this territory besides New York and Boston are Fall River, Providence, New Bedford, New London, Bridgeport, New Haven, Hartford, Worcester, Springfield, Willimantic and Pawtucket. [38] Colonel Abbott, U. S. A., one of the leading Chiefs of Engineers who constructed the U. S. harbor defenses, stated that the fire of the sixteen mortars, “like one giant musket throwing a charge of buckshot, each pellet weighing ¼ ton,” could drop their sixteen projectiles into a space 800 feet long by 300 feet wide. The author was present at a test of a 16-mortar battery on Sandy Hook when the sixteen shells were fired simultaneously at a deck-plan of the United States cruiser _San Francisco_, the plan being outlined with stakes on the New Jersey beach five and a half miles from the battery. Each projectile struck inside of the staked outline. [39] “It will thus be seen that there are now provided about one-fourth of the officers and one-half of the enlisted men necessary for this purpose,” i.e. manning the defenses of the American coast--Report, Chief of Coast Artillery, U. S. A., to Chief of Staff, September 19, 1914. [40] “It is certain that present-day coast defenses could not withstand an energetic attack from the land side,” i.e. they must be defended with a mobile army--“Over-Seas Operations.” [41] The present war has made evident to military observers that in the future the “aeroplane screen” will play a vital part similar to the “cavalry screen.” It is based on the simple principle of overpowering the adversary’s attempts by vastly superior numbers.