Hydra 70

Hydra 70

Four dummy Hydra 70 rockets and an inert AGM-114 Hellfire
Type Rocket
Place of origin United States
Service history
In service 1948–present[1]
Used by See Users
Production history
Unit cost $2,799[1]
Weight 13.6 lb (6.2 kg) (Mk 66 Mod 4 rocket motor only)[2]
Length 41.7 in (1,060 mm)
Diameter 2.75 in (70 mm)

Muzzle velocity 2,300 feet per second (700 m/s)
Effective firing range 8,700 yards (8,000 m)
Maximum firing range 11,500 yards (10,500 m)

Speed 2,425 ft/s (739 m/s)
AH-64 Apache, AH-1Z Viper, AH-1 Cobra, OH-58 Kiowa, T-129, Eurocopter Tiger, A-10 Thunderbolt II, UH-60 Black Hawk, P-3 Orion, MH-6 Little Bird, F-16 Fighting Falcon, F/A-18 Hornet, AV-8B Harrier II[2]

The Hydra 70 rocket is a 2.75-inch fin-stabilized unguided rocket used primarily in the air-to-ground role. It can be equipped with a variety of warheads, and in more recent versions, guidance systems for point attacks. The Hydra is widely used by US and allied forces, competing with the Canadian CRV-7 which is physically interchangeable.


The Hydra 70 is derived from the 2.75-inch Mk 4/Mk 40 Folding-Fin Aerial Rocket developed by the United States Navy for use as a free-flight aerial rocket in the late 1940s. The Mk 40 was used during the Korean and Vietnam wars, being used to provide close air support to ground forces from about 20 different firing platforms, both fixed-wing and armed helicopters.

The main change made to produce the Hydra was the Mk. 66 motor which uses a new propellant that offers considerably more thrust, 1,335 pounds-force (5,940 N) (Mod 2/3) 1,415 pounds-force (6,290 N) (Mod 4). The fins of the Mk 40 flipped forward from the rear when the rocket left the launching tube, but in the Hydra they are curved to match the outside diameter of the rocket fuselage and flip sideways to open, which is referred to as WAFAR (Wrap-Around Fin Aerial Rocket) instead of FFAR (folding-fin aerial rocket). To improve stability during the time while the fins are still opening, the four motor nozzles have a slight cant angle to impart a spin while the rocket is still in the launch tube.

Today, the OH-58D(R) Kiowa Warrior and AH-64D Apache Longbow, as well as the Marine Corp's AH-1 Cobra, carry the Hydra rocket launcher standard on its weapon pylons.[3][4]

Mk 66 rocket motor variants

Designation Description
Mk 66 Mod 0 70 mm (2.75 in) WAFAR universal motor; common motor for the GD Hydra 70 series of rockets; original prototype; for US Army
Mk 66 Mod 1 Mk 66 variant; production variant; for US Army
Mk 66 Mod 2 Mk 66 Mod 1 variant; HERO (Hazards of Electromagnetic Radiation to Ordnance) safe; for US Navy and US Air Force
Mk 66 Mod 3 Mk 66 Mod 1 variant; HERO safe; Mk 66 Mod 2 for US Army
Mk 66 Mod 4 Mk 66 Mod 2/3 variant; incorporates a Salt rod to reduce exhaust gases; for all services
Mk 66 Mod 5 Mk 66 Mod 4 variant; Incorporates propellant venting during fast cook off
Mk 66 Mod 6 Mk 66 Mod 4/5 variant; designed to reduce the tendency of secondary launch gasses to combust in the parent aircraft’s engine, primarily with the AH-64 helicopter


Hydra 70 rockets on an AH-1 Cobra helicopter

The family of Hydra 70 (70 mm) 2.75 inch rockets perform a variety of functions. The war reserve unitary and cargo warheads are used for anti-materiel, anti-personnel, and suppression missions. The Hydra 70 family of folding-fin aerial rockets also includes smoke screening, illumination, and training warheads. Hydra 70 rockets are known mainly by either their warhead type or by the rocket motor designation, Mk 66 in US military service.

United States

In the U.S. Army, Hydra 70 rockets are fired from the AH-64A Apache and AH-64D Apache Longbow helicopters using M261 19-tube rocket launchers, and the OH-58D Kiowa Warrior using seven-tube M260 rocket launchers. In the U.S. Marine Corps, either the M260 or M261 launchers are employed on the AH-1 Cobra and future AH-1Z Viper, depending upon the mission. The M260 and M261 are used with the Mk 66 series of rocket motor, which replaced the Mk 40 series. The Mk 66 has a reduced system weight and provides a remote fuze setting interface. Hydra 70s have also been fired from UH-60 and AH-6 series aircraft in US Army service.

The AH-1G Cobra and the UH-1B "Huey" used a variety of launchers including the M158 seven-tube and M200 19-tube rocket launchers designed for the Mk 40 rocket motor; however, these models have been replaced by upgraded variants in the U.S. Marine Corps because they were not compatible with the Mk 66 rocket motor. The Hydra 70 rocket system is also used by the U.S. Navy, and the U.S. Air Force.

Common U.S. Mk 66 compatible launchers

Dummy Hydra 70s in an M261 launcher on a Dutch AH-64 Apache. The tips of some of the rockets are white (and the rockets are shorter in length, and they are attached to the launcher via umbilical connectors) because they have a different type of warhead and fuze.
Designation Description
M260 7-Tube LWL (LightWeight Launcher)
M261 19-Tube LWL (LightWeight Launcher)
LAU-130/A 19-Tube rocket launcher
LAU-131/A 7-Tube rocket launcher
LAU-68D/A 7-Tube LAU-68C/A variant; compatible w/ Mk 66 rocket motor; external thermal protection coating; launcher supports single and ripple firing
LAU-61C/A 19-Tube LAU-61B/A variant; compatible w/ Mk 66 rocket motor; external thermal protection coating; launcher supports single and ripple firing


Hydra 70 warheads fall into three categories:

Fuzing options

# Designation Description Arming Range, Acceleration or Time
1 M423 Nose Mount, Point Detonating for slow speed platforms (helicopters) 47 to 102 yards (43 to 93 m)
2 M427 Nose Mount, Point Detonating for high speed platforms 197 to 466 yards (180 to 426 m)
3 XM436 Air burst, Motor-Burnout Delay
4 XM438/M438 Nose Mount, Point Detonating
5 M440 Point Detonating
6 Mk 352 Mod 0/1/2 Point Detonating
7 M429 Proximity Air burst
8 M433 Nose Mount, Resistance Capacitance (RC) SuperQuick (PD) 11 to 49 yards (10 to 45 m) Delay in 5.5 yards (5.0 m) increments including 3.3 yards (3.0 m) Bunker penetrating option
9 M439 Base Mount, Resistance Capacitance (RC), Payload Discharging Pilot-Selectable Discharges SMs between 547 and 7,874 yards (500 and 7,200 m) (766 to 7,546 yards [700 to 6,900 m] on AH-1s) 27Gs
10 M442 Air burst, Motor-Burnout Delay Discharges Flare at 3,281 yards (3,000 m), 17-22 g required for arming
11 M446 Base Mount, Air burst, Motor-Burnout Delay
12 Model 113A Base Mount, Air burst, Motor-Burnout Delay

Common warheads

The most common warhead for the Hydra 70 rocket is the M151 "10-Pounder," which has a blast radius of 10 meters and lethal fragmentation radius of around 50 meters.[5]

Designation Description Weight Payload Fuze Type Fuzing options
M151 High explosive (HEPD) '10 pounder' 8.7 pounds (3.9 kg) (w/o Fuze) 2.3 pounds (1.0 kg) Comp B-4 HE M423 1,2,5,7,8
M156 White phosphorus munitions (WP) 9.65 pounds (4.38 kg) 2.2 pounds (1.00 kg) WP M423 M429 1,2,6,7
M229 High explosive (HEPD); elongated M151 '17 pounder' 17.0 pounds (7.7 kg) (Fuzed) 4.8 pounds (2.2 kg) Comp B-4 HE M423 1,2,6,7
XM245 Submunition warhead possibly a modernized XM80/XM99 32 XM100 CS canisters 3
M247 High-explosive anti-tank (HEAT)/high-explosive dual purpose (HEDP) 8.8 pounds (4.0 kg) 2.0 pounds (0.91 kg) Comp B HE M438 PD 4 (integral to warhead)
M255 APERS (anti-personnel) warhead 2500 28 grains (1.8 g) flechettes 9
M255E1/A1 Flechette warhead 14.0 pounds (6.4 kg) 1179 60 grains (3.9 g) flechettes M439 9
M257 Parachute illumination 11.0 pounds (5.0 kg) One M257 Candle (Flare) 1 million candela M442 10 (integral to warhead)
M259 White phosphorus (WP) 9
M261 Multi-purpose submunition (MPSM) 13.5 pounds (6.1 kg) 9 M73 (Grenade) Submunitions M439 with M84 electric detonator 9
M264 Red phosphorus (RP) Smoke 8.6 pounds (3.9 kg) 72 RP Pellets M439 9
M267 MPSM Practice 13.5 pounds (6.1 kg) Three Marking SMs, 6 Metal Weights M439 with M84 electric Detonator 9
M274 Practice (Smoke) 9.3 pounds (4.2 kg) 2 ounces (57 g) of potassium perchlorate and aluminum powder M423 1
M278 Infra-red (IR) parachute illumination 11.0 pounds (5.0 kg) One M278 IR Flare M442 10 (integral to warhead)
Mk 67 Mod 0 White phosphorus (WP) 1,2,6,7
Mk 67 Mod 1 Red phosphorus (RP) 1,2,6,7
WTU-1/B Practice 9.3 pounds (4.2 kg) Inert None None
WDU-4/A APERS warhead 9.3 pounds (4.2 kg) 96 flechettes of unknown weight 12 (integral to warhead)
WDU-4A/A APERS warhead 9.3 pounds (4.2 kg) 2205 20 grains (1.3 g) flechettes 12 (integral to warhead)

NOTE: Though some of the warheads described were designed for the older Mk 40 rocket motor, but most likely could work with the Mk 66 motor if upgraded or modernized models were not available. However, this would not be necessary, as vast quantities of upgraded models exist today.

Mk 66 rocket motor technical data

Weight: 13.6 pounds (6.2 kg)

Length: 41.7 inches (1,060 mm)

Burn time: 1.05–1.10 sec

Average thrust (77 F):

Motor burnout range: 1,300 feet (400 m)

Motor burnout velocity: 2,425 ft/s (739 m/s)

Launch spin rate: 10 rps, 35 rps after exiting launcher

Velocity at launcher exit: 148 ft/s (45 m/s)


Effective Range: 547 to 8,749 yards (500 to 8,000 m) depending on warhead and launch platform

Maximum Range: 11,483 yards (10,500 m) under optimum conditions

Precision guided Hydra 70

There are several design efforts to turn the Hydra 70 rocket into a precision guided munition (PGM) to produce a weapon with greater accuracy but at less cost than other guided missiles. These include:

The APKWS was the first to be fielded in March 2012,[8] and the TALON entered full rate production for the United Arab Emirates Armed Forces in September 2014.[9]

Roketsan Cirit is a similar missile compatible with 70 mm rocket launchers, but it was developed from scratch and doesn't use Hydra 70 components.[10]


Map with Hydra 70 operators in blue

Current operators

See also


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