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The coast defense mortar was a massive weapon of 12-inch (305 mm) caliber emplaced during the 1890s and early 20th century to defend U.S. harbors from seaborne attack.〔There was also a 13-inch (330 mm) smooth-bore muzzle-loading mortar, used during the Civil War (see Siege artillery in the American Civil War) and for about 15 years thereafter, which, although often used against land targets, was also called a "coast defense mortar".〕 In 1886 when the Endicott Board set forth its plan for upgrading the coast defenses of the United States, it relied primarily on mortars, not guns, to defend American harbors.〔The Board recommended "581 high power guns of heavy calibers and 724 heavy rifled mortars. In a total of 1,305 heavy guns, 55.5% () mortars." See "Sea-Coast Mortar Fire," Report of a Board, in ''Journal of the United States Artillery'', Vol. 7, No. 3, 1897.〕 Over the years, provision was made for fortifications that would mount some 476 of these weapons, although not all of these tubes were installed.〔Nevertheless, a quick search of the web indicates that this weapon was the largest caliber and most widely deployed mortar in service anywhere in the world.〕 Today, the only remaining mortars of this type in the 50 states are four at Battery Laidley, part of Fort Desoto in St. Petersburg, Florida, but the remains of coast defense mortar emplacements can be seen at many former Coast Artillery forts across the United States and its former territories. Additional 12-inch mortars and other large-caliber weapons remain in the Philippines. ==The weapons== The 1890 M1 (Model 1) 12-inch mortar was one of the most powerful coast artillery pieces of its era, and was the most common type emplaced to guard U.S. harbors. This mortar and other models, the M1886, M1908, and M1912, usually fired deck-piercing (also called armor-piercing) shells. These weighed from and had heavy, hardened steel caps, designed to pierce a ship's deck armor before the shell exploded.〔See Bolling W. Smith, "Coast Artillery Projectiles, 1892-1915," The Coast Defense Study Group Journal, Vol 9, No. 1, February, 1995. p.16.〕 These mortars, firing the half-ton shells at an elevation of 45 degrees, had a range of (about 7 miles).〔See "The Service of Coast Artillery," Frank T. Hines and Franklin W. Ward, Goodenough & Woglom Co., New York, 1910, p. 119.〕 The deck-piercing shells were usually the ammunition of choice, because even the heaviest battleships of the 1890-1920 period were relatively lightly armored on the tops of their main decks, so a plunging half-ton shell could inflict crippling damage on one of them.〔The half-ton deck-piercing mortar shells could penetrate between of armor plate, depending upon the maximum height to which they were shot. Since shells shot at close range did not travel high enough to attain deck-piercing momentum, these mortars were generally not effective at close range. See Smith, supra, Note No. 3〕 Early on (from about 1890 to 1915), coast defense mortars were also supplied with so-called "torpedo shells" weighing . (see illustration at right, below). These were thin-walled shells roughly in length that carried explosive charges of about and were meant to detonate upon contact with the deck of a ship, scattering fragments among the crew. The M1890M1 mortar was most often installed on an M1896 carriage (as shown here in the images at top left and right).〔The M1896 carriage had massive recoil springs that extended into a circular pit below the mortar's circular base (which was 14 ft in diameter). At almost all the former mortar batteries in the U.S., however, these mounting pits have now been filled in and capped with concrete, leaving only a "new-ish" concrete circle to mark the former position of the mortar.〕 The mortar and its carriage weighed a total of 78.5 tons. The carriage was geared to enable it to be turned (in azimuth) by means of a traversing crank with two handles, located on the right side of the piece. A ring marked in degrees of azimuth ran around the mortar, just outside the inner steel circle or "racer" that carried the carriage, and a soldier read a pointer on the racer to aim the mortar in direction.〔A crew man was tasked with using chalk to mark on the azimuth circle each new azimuth that was fired, a step that was supposed to help avoid hoped mistakes in aiming the piece.〕 The tube was raised or lowered (in elevation) by twin geared wheels with long spokes (resembling ship's wheels) that were located on either side of the carriage. The breech could be rapidly depressed to an almost level position for loading and then be quickly elevated for firing.〔A built-in interlock protected the mortar from being fired if its elevation was less than 42 degrees, preventing it from being fired at the wall of its emplacement.〕 Other carriages included the M1891 and M1908.〔Berhow, pp. 134-135, 140-145, 152-153〕 In addition to the elevation of its tube, the factor that determined the mortar's range was the size of the powder charge that was loaded into its breech, following the shell. The desired range for the mortar was specified in terms of zones. The smallest zone (shortest range) was Zone 1, and the largest (longest range) was Zone 9. With the so-called "aliquot charge" (shown in the photo at right), up to 9 equal-sized, disk-shaped bags of powder (each about thick and containing of powder) could be attached to a 10th (or "base") bag, by means of cloth binding straps that were sewn to the base bag. Often the base bag was painted red, indicating that the powder assembly was to be loaded into the breech "red end last," so that it bumped up against the closing breech block (or faced the gunner). The red base bag also contained a small charge of black powder as an igniter. When the breech was closed, a detonator was inserted through the breech block and contacted the igniter, ready to set off the full powder charge. The mortar could be fired in one of two ways: either electrically or manually (by the pull of a lanyard). And each method had its own type of detonator (electrical or friction). Electrical firing required first that the crew attach a wire to the electrical detonator, which protruded from the breech block. Second, the crew had to connect the firing cable coming out of the pit floor to the carriage of the individual mortar, out in the pit. Third, the circuit switch (usually located on the wall of the pit near the data booth) leading to the individual mortar had to be thrown into the closed (firing) position. Finally, the firing magneto, which was mounted on a special "shoe", often on the wall of the pit near the data booth, had to be cranked up and then released, sending the firing current out to the pit. Depending on the switch settings, the mortars in a given pit could be fired one at a time or all together. Lanyard firing had fewer fail-safe features, and was accomplished by a crewman who stood well behind the breech and pulled smartly on the lanyard to fire the individual mortar. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「12-inch coast defense mortar」の詳細全文を読む スポンサード リンク
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