Hydra 70

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Hydra 70
AGM-114 and Hydra 70.jpeg
Four dummy Hydra 70 rockets and an inert AGM-114 Hellfire
Type rocket
Place of origin United States
Service history
Used by United States, United Kingdom, Colombia, Japan, Kuwait, the Netherlands, Singapore, Thailand, and United Arab Emirates
Weight 13.6 lb (6.2 kg)[dubious ]
Length 41.7 in (1,060 mm)
Diameter 2.75 in (70 mm)

Muzzle velocity 700 m/s (2,300 ft/s)
Effective firing range 8,000 m (8,700 yd)
Maximum firing range 10,500 m (11,500 yd)

Speed 2,425 ft/s (739 m/s)
AH-64 Apache, AH-1 Cobra, OH-58 Kiowa, Eurocopter Tiger

The Hydra 70 rocket is a weapon derived from the 70 mm (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 Hydra 70 family of WAFAR (Wrap-Around Fin Aerial Rocket), based on the Mk 66 universal motor, was developed from the previous 2.75 inch Mk 40 motor-based folding fin aerial rocket. The propellant grain is longer and of a different formulation than that of the MK40/MK4, however, the stabilizing rod and igniter are essentially the same design. The MK66 motors have a substantially higher thrust, 1335 lbs (Mod 2/3) 1415 lbs (Mod 4), and a longer range than the older motors. To provide additional stability the four rocket nozzles are scarfed at an angle to impart a slight spin to the rocket during flight. The Mk 40 was used during the Korean and Vietnam wars, beginning a rich history of providing close air support to ground forces from about 20 different firing platforms, both fixed-wing and armed helicopters, by all US armed forces. 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.[1][2] The name Hydra is a reference to the beast of Greek mythology.

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

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Hydra 70 rockets on a 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.


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 H-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.

Hydra 70 rockets may also be used from the following fixed-wing platforms: A-4, A-6, A-7, AV-8B, A-10, F-4, F-16, F/A-18 and OV-10.

Common U.S. Mk 66 compatible launchers

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) because they have a different type of fuse/warhead.
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:

  • Unitary warheads with impact-detonating fuses or remote-set multi-option fuses.
  • Cargo warheads with air burst-range, with setable fuses using the "wall-in-space" concept or fixed standoff fuses.
  • Training warheads.

Fusing options

# Designation Description Arming Range, Acceleration or Time
1 M423 Nose Mount, Point Detonating for slow speed platforms (helicopters) 43 to 93m
2 M427 Nose Mount, Point Detonating for high speed platforms 180 to 426m
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) 10 to 45m Delay in 5m increments including 3m Bunker penetrating option
9 M439 Base Mount, Resistance Capacitance (RC), Payload Discharging Pilot-Selectable Discharges SMs between 500 and 7200m (700 to 6900m on AH-1s) 27Gs
10 M442 Air burst, Motor-Burnout Delay Discharges Flare at 3000m, 17-22G required for arming
11 M446 Base Mount, Air burst, Motor-Burnout Delay
12 Model 113A Base Mount, Air burst, Motor-Burnout Delay

Common warheads

Designation Description Weight Payload Fuse Type Fusing options
M151 High explosive (HEPD) '10 pounder' 9.3 lbs (4.2 kg) 2.3 pounds Comp B-4 HE M423 1,2,5,7,8
M156 White phosphorus (WP) 9.65 lbs (4.38 kg) 2.2 lbs (1.0 kg) WP M423 M429 1,2,6,7
M229 High explosive (HEPD); elongated M151 '17 pounder' 17.0 lbs (7.7 kg) 4.8 pounds 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 lbs (4.0 kg) 2.0 lbs Comp B HE M438 PD 4 (integral to warhead)
M255 APERS warhead 2500 28 grain (1.8 g) flechettes 9
M255E1/A1 Flechette warhead 14.0 lbs (6.4 kg) 1179 60 grain (3.8 g) flechettes M439 9
M257 Parachute illumination 11.0 lbs (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 lbs (6.1 kg) 9 M73 (Grenade) Submunitions M439 with M84 electric detonator 9
M264 Red phosphorus (RP) Smoke 8.6 lbs (3.9 kg) 72 RP Pellets M439 9
M267 MPSM Practice 13.5 lbs (6.1 kg) Three Marking SMs, 6 Metal Weights M439 with M84 electric Detonator 9
M274 Practice (Smoke) 9.3 lbs (4.2 kg) 2 ounces of potassium perchlorate and aluminum powder M423 1
M278 Infra-red (IR) parachute illumination 11.0 lbs (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 lbs (4.2 kg) Inert None None
WDU-4/A APERS warhead 9.3 lbs (4.2 kg) 96 flechettes of unknown weight 12 (integral to warhead)
WDU-4A/A APERS warhead 9.3 lbs (4.2 kg) 2205 20 grain (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.[citation needed]

Mk 66 rocket motor technical data

Weight: 13.6 lb

Length: 41.7 in (1.06 m)

Burn time: 1.05 - 1.10 sec

Average thrust (77 F): 1,335 lb (Mod 2/3) 1,415 lb (Mod 4)

Motor burnout range: 1,300 ft (397 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)

Acceleration: 60-70 g (initial) 95-100 g (final)

Effective Range: 500 to 8,000 m depending on warhead and launch platform

Maximum Range: 10,500 m under optimum conditions

Precision guided Hydra 70

The Advanced Precision Kill Weapon System (APKWS) II is a program to provide a laser guided missile that is compatible with the existing Hydra 70 systems in service. It was cancelled by the US Army in February 2007,[3] but was restarted by the US Navy in 2008. Similar programs are the US Navy Low-Cost Guided Imaging Rocket, Lockheed Martin Direct Attack Guided Rocket and the ATK/Elbit Guided Advanced Tactical Rocket – Laser.

See also


  1. ^ "Hydra 70", Munitions, Military, Global Security .
  2. ^ Hydra 70 (PDF), GDATP .
  3. ^ R&D Budget Request (PDF), US Army, 2008, p. 4 .

External links