32. Signal Projector Mk 1 is a mortar-type projector, mounted on deck and used for firing ships emergency indentification signals. It is held in place by three guy cables, one of which is adjustable by means of a turnbuckle. The mortar consists of a 28-inch remo-vable barrel and breech assembly, which fits into a tubular steel barrel holder, and in turn is permanently fixed to an adjustable steel base in the form of a tripod. The barrel is constructed of 0.25-inch steel tubing, which reinforced by another 0.25-inch steel tube from the breech to a point 14.5 inches up the barrel. See Fig. 8. This assembly, including the breech mechanism, is removable and has no fastening in the barrel holder. The barrel holder is also of 0.25-inch tubular steel and extends from the steel base 15 inches up the barrel, where the guy cables are attached. The base and barrel holder assembly is so designed that it can be adjusted for elevation by means of an adjustment bolt and lock-ing nut at the end of the straight leg of the tripod. The adjustable guy cable must be lengthened or shortened to agree with the above cable adjustment. In its normal position the mortar has an elevation of 80 degrees, which may be reduced to a minimum of 75 degrees. The only moving parts of the mortar are th firing pin, the valve head, and the valve stem. The firing pin is press fitted into the center of the valve head, and its shank acts as a valve stem. The valve is of the poppet type, 1.75 inches in diameter and held open by a compression spring. The valve stem, which is also the shank of the firing pin, extends through the breech. The entire mechansim is held together by a collar which fits over the valve stem and is fastened in place by a cotter pin. The valve opens into twel-ve vent holes of 0.125 inches each, so that air is exhausted from the barrel and breech when the signal to be fired is dropped from the muzzle. The barrel is drilled 23 inches from the breech, and a pin is inserted across the bore. This pin is attached a lanyard.

Figure 8. – Signal Projector Mk 1

Loading and Firing

33. Before attempting to load Signal Projector Mk 1, place the cotter pin at the end of the operating lanyrad through the holes in the barrel. See Fig. 9 A. Then place the signal with its percussion cap down in into the muzzle (see Fig. 9 B), letting it down gently un-til it rests on the cotter pin. See Fig 9 C. The take the free end of the lanyard and carry it away from the mortar, taking case that the lanyard does not foul on any part of the deck equipment. At the command to fire pull the lanyard with increasing steadiness; do not jerk it. Caution: If the signal fails to fire, count to 30 slowly before reloading, or allow 30 seconds before approaching the mortar. To reload, it woll be necessary to remove the barrel from the barrel-holder and invert it. Be sure to catch the undischarged signal as it comes out from the muzzle and lay it aside for disposition as outlined in para-graph 17.

Figure 9. – Steps in Loading Signal Projector Mk 1 Mod 0

Disassembly and Assembly

34. To disassembly the barrel and breech assembly of Signal Projector Mk 1, remove it from the barrel-holder and take the following steps:

(a) Unscrew the brass breech obturating cap.

(b) Remove the cotter pin from the collar on the valve stem. Then invert the breech, and the valve and spring will drop out. See Fig. 8.

(c) As the valve stem is also part of the firing pin and is press fitted into the valve head, it may be necessary to tap it lightly with a plastic hammer to remove it from the head.

To assemble, reverse the above order, making certain that the valve spring is in its pro-per place and also that a slight pressure operates the valve, before screwing the breech on the barrel.

Safety Precautions

35. Because Signal Projector Mk 1 is a missile-throwing gun, and contains a charge which is approximately twice as great as a shotgun charge, the following safety measures must be taken:

(a) The projector must be pointed in a direction well out of range of all other craft. The signal spins end-over-end when fired, and ejection of the signal components from the case may be in any direction. The reaction of the ejection charge gives the signal case considerable impetus in the opposite direction, before it falls base-down as a missile. For the above reasons, the prokjector should usually not be fired at an angle of less than 80 - 85 degrees. Ships carrying two projectors should always fire from the leeward side.

(b) Signals are subject to misfire and hand fire, just as any other percussion primed am-munition. Care must be taken not to drop a second signal down the projector on top of an unfired signal.

(c) Before firing, the projector should be inspected to insure the working of the valve, which should be open before the projector is fired. If it is closed, an air cushion will pre-vent the signal from sliding down at sufficient speed. On the other hand, should the val-ve jam from lead chips or other foreign matter, the pressure will deplete so rapidly that the signal will rise only 50 to 100 feet. The signal is designed so that its lead pressure retaining disc will rupture, rather than shear. The lead pressure disc may shear in occa-sional signal firings causing small lead discs to be left in the breech above the valve. Ac-cumulation of such discs at the base of the mortar will result in misfire.

(d) The primer of a fired signal occasionally may be blown from the base and will remain in the breech above the valve mechanism. In such cases, the next signal will not fire. It is then necessary to remove the signal and to clean the valve mechanism before firing again.

(e) In operation, the projector barrel should be lifted out whenever the opportunity oc-curs and the breech turned up. This will dislodge any accumulations in the breech. Inas-much as the smokeless powder propellant of the signal leaves residue on the walls of the barrel, the latter should be disassembled after each five rounds and cleaned by drawing thorugh it a piece of waste cloth dipped in acetone or some other solvent. Failure to do this will retard the fall of the signal down the barrel and may result in frequent misfires.

(f) Warning: Cleaning with abrasive, or corrosion, will enlarge the bore of the pro-jector. This, in turn, materially affects the height to which signals are projected, and may also rupture the obturating cup. The bore and working parts of the projector should be protected with a film of light oil during protracted standby periods when it is mounted on deck.