This consists of a row of heavy beams planted across a channel similar to a “chevaux de frise.” The inner ends of the beams are securely anchored to the bottom, the latter giving them a support when they are ran into. The outer ends carry each a single torpedo shaped like a large rifled shell and holding from 60 to 100 lbs. of powder; bolted to it so that the tops of the torpedoes are about eight or ten feet below water. These ends are moored so as not to swing about too much in the current. Just under the outer ends a frame is constructed to support the beams in case they get waterlogged. Contact-fuses are used with these torpedoes, and the whole arrangement serves the double purpose of acting as a torpedo and as a construction defence. These beams are also used singly in many cases. [Illustration: Frame-Torpedoes.] _Brooks’s Torpedo._ This form of torpedo is intended to baffle attempts at removal by sweeping with drags and grapnels. The beam used in this case is of a length sufficient to allow the top of the torpedo to be at the proper distance below water when it is vertical. The heel of the spar is shod with a pointed iron casing having a ring in the end connected to an anchor-shackle, the anchor being completely buried. In this manner the beam is free to oscillate. The torpedo, which is conical with a dome cover, ships on the upper end of the beam, all sharp corners and edges where a rope or grapnel might catch being avoided. In the top of the torpedo are placed five contact-fuses. In order to make this torpedo still more difficult of removal, it is placed in connection with a heavy ground-torpedo called a turtle-back in such a manner that any attempt to remove it from its berth causes the explosion of the turtle-back. _Singer’s Torpedo._ This torpedo contains an air-chamber in the upper part, whilst all the lower portion is devoted to the charge, varying in weight from 50 to 100 lbs. of powder. On top of the case is a heavy conical iron cover loosely secured, so that if the torpedo is struck a violent blow or is canted well over it will fall off. This cover is secured by a wire to a mechanical fuse (there are several different types) in such a way that the jerk given to the wire when the cover falls off will explode it. [Illustration: Brooks’s Torpedo.] [Illustration: Singer’s Torpedo.] [Illustration: Barrel Torpedo.] _Barrel Torpedoes._ Barrels are frequently used as torpedoes, being thoroughly caulked and pitched and strengthened as much as possible. They are slung with rope or chain slings, moored in position, and exploded either by contact or electrical fuses. In the majority of cases with defensive torpedoes at present, they are so arranged as to be fired either by contact or at will. TORPEDO-FUSES. Torpedo-fuses may be classified under four different heads; viz., Percussion, Friction, Chemical, and Electric.