Aircraft gun systems have changed significantly over the years. The Navy's high-speed, computer- controlled gun systems are almost futuristic when compared to the mounted machine guns used on the biplanes of the early 1900's. The old Mk 12, 20-mm aircraft gun installed in the A-4 aircraft and operated by a  gas-blowback  system  is  primitive  by  today's standards. Today's gun systems must meet demanding performance requirements and provide the firepower needed to penetrate and destroy advanced enemy targets. The M61A1, 20-mm automatic gun system is the most widely used gun system in Navy aircraft. The M61A1 20-mm automatic aircraft gun (fig. 8-20) is a six-barrel rotary-action mechanism based on the early Gattling gun. It is a revolving cluster of barrels fired once per each revolution. The gun is hydraulically driven and electrically controlled by the aircraft's weapons control systems. The gun is capable of firing 4,000 to 7,200 rounds of M50 (series) ammunition per minute. As installed in Navy aircraft, the gun has two pilot-selectable firing rates of 4,000 (gun low) or 6,000 (gun high) rounds per minute. Ammunition is supplied to the gun by the ammunition handling and storage system. The system is an endless conveyor belt (closed loop). Ammunition is transported from the ammunition drum to the gun, and expended casings and unfired rounds are returned to the drum. Although the component's physical location may vary between gun installations, the function and operation of the system are basically the same. Q8-20. What is the most widely used gun system in Navy aircraft? SIGNALING, MARKING, AND ILLUMINATION DEVICES LEARNING OBJECTIVE: Identify the types, uses, and basic characteristics of signaling, marking, and illumination devices. Signaling, marking, and illumination devices are used by the Navy for various purposes. Some are used as signals by downed aircraft, while others are launched by aircraft. PYROTECHNICS Pyrotechnics are "fireworks adapted to military use." The word   pyrotechny   means "the art of fire." Pyrotechnics are items that produce their effect by burning and are consumed in the process. As used in the military, pyrotechnics are burning items that produce a bright light for illumination. They also produce colored lights or signaling smoke. All of the pyrotechnic devices described here contain combustible chemicals, which when ignited produce a flame, flash, smoke, or a combination of these effects. Because of the many pyrotechnics available, only those items that an Airman may see on a routine basis are covered. 8-19 COUPLING CLAMP END PLATE HOUSING COVER HOUSING COVER PIN HOUSING ASSEMBLY FIRING CONTACT RECOIL ADAPTER MID-BARREL CLAMP BARREL MUZZLE CLAMP GUIDE BAR CLEARING SECTOR CLEARING SOLENOID VIEW A VIEW A INDEXING PIN ANF0820 Figure 8-20.—M61A1 20-mm automatic aircraft gun.