The F-15E´s fixed armament consists of one General Electric (now General Dynamics Armament Systems) M61A1 Vulcan 20mm Gatling rotary gun. The gun is mounted in the aircraft´s starboard wing root. The muzzle is positioned well aft of the main engine air intake to prevent ingestion of exhaust gases.

The primary use of the gun is in the extremely short range (less than 2,000 feet) air-to-air environment, where more sophisticated air-to-air missiles are ineffective. Alternately, the gun has limited usefulness in a ground strafing role.

The gun has six barrels, weighs 275 pounds and is electrically controlled. Its is driven by the aircraft´s hydraulic system and has a maximum rate of fire of up to 7,200 shots per minute (spm). The firing rate is selectable at 4,000 spm or 6,000 spm.

Each of the gun´s six barrels fires only once during each revolution of the barrel cluster. This principle contributes to long life by minimizing barrel erosion and heat generation.

When looking on the F-15E´s gun muzzle from the front, the gun fires from the 9 o´clock (farthermost left) barrel position. The gun muzzle aperture housing is made of titanium. This metal resists the heat from the muzzle blast. The muzzle velocity of the M61A1 gun is 3,380 feet per second.

In order to gain additional space for electronic equipment, primarily the AN/ALQ-135/B Internal Countermeasures System, the F-15E has a redesigned ammunition handling system that uses a linkless feed system. In contrast to the 940 rounds of ammunition carried by previous F-15 variants, the F-15E´s ammunition capacity is limited to 450 rounds.

A storage container assembly provides storage for the 20mm ammunition and is directly linked to the ammunition conveyer system and the return conveyer system. An exit unit removes ammunition from the storage container and an entrance unit returns spent cases, misfired rounds and cleared rounds to the storage container.

The new system required a small fairing on the underside of the aircraft´s fuselage directly beneath the ammunition storage container to reload the system. This fairing is one of the identifying features of the F-15E and its variants.

The M61A1 gun uses M50 series and PGU series 20mm ammunition. The M50 / PGU series consists of various types of cartridges developed for specific applications, including test cartridges, dummy cartridges, target practice, target practice tracer, armor piercing incendiary, and semi-armor piercing, high-explosive incendiary.

The M50 / PGU series 20mm ammunition is loaded into the F-15E´s M61A1 gun system through the linkless ammunition loading system (LALS) series. The LALS transports rounds from the transporter to the aircraft system, and simultaneously transports spent cases and cleared rounds from the aircraft system to the transporter.

20mm Armament System

General Dynamics Armament Systems (GDAS) has worked closely with Boeing to produce a new lightweight linear linkless ammunition feed system which offers configuration flexibility and improved ammunition packaging efficiency. These features provide additional space for other aircraft equipment.

This system is currently in production for concurrent deliveries with F-15E aircraft. The GDAS armament system operates on the same principle as the previous M61A1 gun systems used on the F-15E, but is lighter and has an improved ammunition capacity of 500 rounds compared to 450 rounds of the previous system.

The GDAS lightweight linear ammunition feed system provides high reliability and maximum round capacity for the F-15E´s allotted space envelope. It is the product of over ten years of research and development. The GDAS feed system is fully compatible with all M50 series and the improved PGU series ammunition.

Sources

• US Air Force
• General Dynamics

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