The torpedo, a copper cylinder containing explosive and percussion and primer mechanism, was fired by triggers. It was carried on a boom, twenty-two feet long, attached to the bow. The speed was seldom more than four miles an hour on a calm day. As there was no means of replenishing the air other than by coming to the surface and lifting one of the hatchways, it was obviously a fair-weather ship. On the afternoon of the 17th February, 1864, the _Hunley_ set out on her final trip. While attacking the submarine was only partly submerged, and one of the hatches was uncovered; why will never be known. She made straight toward the _Housatonic_, with the evident intention of striking the vessel near the magazines with her torpedo. There was an explosion, the ship heeled to port, and went down by the stern. When divers examined the extent of her injuries the plucky little _Hunley_ was found with her nose buried in the gaping wound in her victim’s hull. Her crew were dead, but apparently the officer was saved. Other submarines or partly submersible boats were used by the defenders of the Southern cause. They were usually termed ‘Davids’ because they were built to sink the Goliaths of the Federal Navy. The _New Ironsides_, the _Minnesota_, and the _Memphis_ were all damaged as a result of their operations. The only weapon of the submerged submarine is the torpedo. The World War brought no surprise in this direction. For surface work the calibre of the guns mounted on the disappearing platforms has increased very considerably. In 1914 a 14–pdr. was considered ample armament. With added displacement, gun-power has grown enormously. Some German underwater craft in 1918 carried 5.9–in. guns—that is to say, weapons larger than those used by many destroyers. During the past decade torpedoes and submarines have made almost parallel progress. Of the various types of the former, the Whitehead is first favourite in the Navies of Great Britain, Japan, Russia, and Austria-Hungary, while France uses both the Whitehead and the Schneider, and Germany was exclusively devoted to the Schwartzkopf (Blackhead). The extreme effective range of each may be taken as from 10,000 to 12,000 yards. The essential difference between a torpedo and the usual run of naval ammunition for guns is that the torpedo retains its propellant, while the shell does not. The torpedo is really an explosive submarine mine forced through the water at a rate varying from 28 knots to 42 knots by twin-screws worked by compressed air engines. Any deviation from the course is automatically corrected by a gyroscope. Some torpedoes are now fitted with an apparatus which causes the torpedo to go in circles should it miss its mark and meet with the wash of passing ships. There is the added possibility, therefore, that the weapon may strike a vessel at which it was not aimed when a squadron is proceeding in line ahead.