The Mk 4 Folding-Fin Aerial Rocket (FFAR) is a 2.75 in (70 mm) diameter unguided rocket weapon commonly used by U.S. military aircraft. It was intended as an air-to-air weapon to allow interceptor aircraft to shoot down enemy bombers with greater range and effectiveness than machine guns or cannon. It was later developed into a modular rocket motor for air-to-ground use.

History

The advent of jet engines for both fighters and bombers posed new problems for interceptors. With closing speeds of 1,500 ft/s (457 m/s) or more for a head-on interception, the amount of time available for a fighter pilot to successfully target an enemy aircraft and inflict sufficient damage to bring it down was vanishingly small. Wartime experience had shown that .50 caliber (12.7 mm) machine guns were not powerful enough to reliably down a bomber, certainly not in a single volley, and heavy cannon did not have the range or rate of fire to ensure a hit. Unguided rocket weapons had been proven effective in ground-attack work during the war, and the Luftwaffe had shown that volleys of rockets could be a potent air-to-air weapon as well.

The FFAR was developed in the late 1940s by the US Navy Naval Ordnance Test Center and North American Aviation, based on the German R4M rocket (used by the Messerschmitt Me-262 and others).

The original Mk 4 FFAR was about 4 ft (1.2 m) long and weighed 18.5 lb (8.4 kg), with a high-explosive warhead of about 6 lb (2.7 kg). It had four fins that flipped out on launch to spin-stabilize the rocket. Its maximum effective range was about 3,700 yards (3,400 m). Because of its low intrinsic accuracy, it was generally fired in large volleys, some aircraft carrying as many as 104 rockets.

FFARs were the primary armament of many USAF interceptor aircraft in the early 1950s, including the F-86D, F-89, and F-94C. They were also carried by the F-102 Delta Dagger to supplement its guided missile armament.



The Mk 4 was dubbed "Mighty Mouse" in service, after the popular cartoon character.

The Mighty Mouse was to prove a poor aerial weapon. Although it was powerful enough to destroy a bomber with a single hit, its accuracy was abysmal. Its spin rate was not high enough to compensate for the effects of wind and gravity drop, and the rockets dispersed widely on launch: a volley of 24 rockets would cover an area the size of a football field.

As a result, by the late 1950s it had been largely abandoned as an aircraft weapon in favor of the guided air-to-air missiles then becoming available. The Mk 4 found other uses, however, as an air-to-ground weapon, particularly for the new breed of armed helicopter. A volley of FFARs was as devastating as a heavy cannon with far less weight and recoil, and in the ground-attack role its marginal long-range accuracy was less important. It was fitted with a more powerful motor to become the Mk 40. The Mk 40 was a universal motor developed from the Mk 4 2.75 FFAR, and could be fitted with different warheads depending on the mission. Pods (typically carrying seven or 19 rockets) were created for various applications, and a wide variety of specialized warheads were developed for anti-personnel, anti-tank, and target-marking use.

The FFAR has been developed into the modern Hydra 70 series, which is still in service.

US Mk 40 FFAR Launchers

The United States was the primary user of this type of weapon and developed a number of different launching pods for it. Initially pods were intended to be disposed of by launching aircraft, either in flight or on the ground following a mission. With the advent of the armed helicopter, the need for launching pods that were reusable became apparent. Though the rocket was initially developed by the US Navy, the US Air Force and later US Army were most responsible for the development of rocket pods for all services. These pods are described as follows:

• Launchers designated under the US Air Force system:

Designation	Description
LAU-3/A	19-Tube 70 mm (2.75”) rocket launcher
LAU-3A/A	LAU-3/A variant; differences unknown
LAU-3B/A	LAU-3A/A variant; differences unknown; US Army XM159
LAU-3C/A	LAU-3B/A variant; supports single or ripple fire
LAU-3D/A	LAU-3C/A variant; differences unknown
LAU-32/A	7-Tube 70 mm (2.75”) rocket launcher
LAU-32A/A	LAU-32/A variant; differences unknown; US Army XM157A
LAU-32B/A	LAU-32A/A variant; differences unknown
LAU-49/A	7-Tube 70 mm (2.75”) rocket launcher
LAU-51/A	19-Tube 70 mm (2.75”) rocket launcher
LAU-59/A	7-Tube 70 mm (2.75”) rocket launcher
LAU-60/A	19-Tube 70 mm (2.75”) rocket launcher; similar to LAU-3/A series except in the position of the grounding safety device
LAU-61/A	19-Tube 70 mm (2.75”) rocket launcher; US Army M159A1
LAU-61A/A	LAU-61/A variant; differences unknown
LAU-61B/A	LAU-61A/A variant; differences unknown
LAU-68/A	7-Tube 70 mm (2.75”) rocket launcher; US Army M158A1
LAU-68A/A	LAU-68/A variant; differences unknown
LAU-68B/A	LAU-68A/A variant; differences unknown
LAU-68C/A	LAU-68/A variant; differences unknown
LAU-69/A	19-Tube 70 mm (2.75”) rocket launcher; US Army M200A1

• Launchers designated under the US Army system:

Designation	Description
XM141	Launcher, 2.75-inch Rocket, Seven-Tube, Reloadable, Reusable; 7-Tube 70 mm (2.75”) rocket launcher
XM157A	7-Tube 70 mm (2.75”) rocket launcher; not compatible w/ Mk 66 rocket motor; USAF LAU-32A/A
XM157B	XM157A variant; longer launch tubes, capable of further mounting an XM118 dispenser
XM158/M158	Launcher, 2.75-inch Rocket, Seven-Tube, Reloadable, Reusable, Repairable; 7-Tube 70 mm (2.75”) rocket launcher
M158A1	M158 variant; modified hardback mount; USAF LAU-68/A
XM159	Launcher, 2.75-inch FFAR, 19-Tube, Reloadable, Reusable, Not Repairable; 19-Tube 70 mm (2.75”) rocket launcher; USAF LAU-3B/A
XM159B/C	XM159 variants; differences unknown
M159	19-Tube 70 mm (2.75”) rocket launcher; type standardization of what XM159 unknown
M159A1	M159 variant; differences unknown; USAF LAU-61/A
XM200/M200	19-Tube 70 mm (2.75”) rocket launcher
M200A1	M200 variant; differences unknown; USAF LAU-69/A
MA-2A	2-Tube rocket launcher

Early UH-1B/UH-1C Gunships had the XM-3 Subsystem using paired 24 round rectangular launchers mounted near the back edge of the sliding side doors. These pods were ground reloadable and were semi-permanent aircraft parts. The mounting point had been used to mount booms for 3 SS-11 Launchers on each side for anti-tank missions. The co-pilot had a roof mounted sight and control box to fire these. Later UH-1C and D aircraft had a mount on each side to carry a 7 round pod coupled with paired M-60D machine guns. Some carried M-134 Miniguns with 3000 rounds per gun instead, though these aircraft were normally used by Air Cavalry units, not the Aerial Rocket Artillery (ARA) units.

Also various ground launchers using discarded aircraft pods were used for fire base defence. A towed 6 x 19 round pod configuration called a Slammer was tested for airborne infantry support. The range was approximately 7000 meters using Hydra 70 family rockets.

Warheads for the Mk 40 Motor

With the development of the Mk 40 Mod 0 universal motor came the development of a considerable number of different warheads, as well as, a number of different fuzing options. A list of those warheads believed to be developed before the replacement of the Mk 40 motor with the Mk 66 motor is as follows:

Fuzing Options

#	Designation	Description
1	M423	Point Detonating
2	XM438/M438	Point Detonating
3	Mk 352 Mod 0/1/2	Point Detonating
4	M429	Proximity Airburst
5	M442	Airburst, Motor-Burnout Delay
6	Model 113A	Airburst, Motor-Burnout Delay

US military Warheads

Designation	Description	Fuzing Options
XM80	Submunition warhead w/ 32 XM100 CS canisters	Unknown, believed to have an integral fuze
XM99	Submunition warhead w/ 32 XM100 CS canisters; simplified XM80	Unknown, believed to have an integral fuze
M151	High Explosive (HE)	1,3,4,5
M152	High Explosive (HE) w/ red smoke marker	1,3,4,5
M153	High Explosive (HE) w/ yellow smoke marker	1,3,4,5
M156	White Phosphorus (WP)	1,3,4,5
XM157	Red smoke; unknown compound	1,3,4,5
XM158	Yellow smoke; unknown compound	1,3,4,5
M247	High-Explosive Anti-Tank (HEAT)/High-Explosive Dual Purpose (HEDP)	2 (Integral to Warhead)
M257	Parachute Illumination	5 (Integral to Warhead)
Mk 67 Mod 0	White Phosphorus (WP)	1,3,4,5
Mk 67 Mod 1	Red Phosphorus (RP)	1,3,4,5
WDU-4/A	APERS warhead w/ unknown number of flechettes of unknown weight	11 (Integral to Warhead)

See also

• List of rockets
• List of modern weapons
• Hydra 70
• CRV-7
• Aerial Rocket Artillery
• List of U.S. Army Rocket Launchers By Model Number

References