GDR 99 - Missile Systems

Apaches
Reach Out for Hydra


Section Articles
• Countering Proliferation • Oerlikon Aerospace • Hypersonics: a New Age Dawns • Hi-Tech, Low Cost • The Imperative of Interoperability • ARC Enjoys Rocketing Growth • Apaches Reach Out for Hydra • Aiming High: Raytheon's FMRAAM • Meteoric Rise: Matra BAe's Meteor
Top: In most scenarios, most Apache pilots fly with a mixture of rockets and Hellfire to increase their attack options

Tim Ripley profiles a hard-hitting family of rockets that have proved their worth in battle conditions and secured high praise from Apache fighters.

When the US Army fielded the AH-64A Apache in the mid-1980s it also introduced a new family of unguided rockets to replace its Vietnam vintage ordnance. Although often overshadowed by the laser-guided AGM-114 Hellfire mission, US Army Apaches used the 2.75 inch Hydra 70 family of folding-fin aerial rockets (FFAR) extensively in Operation Desert Storm to great effect. Indeed almost four times as many rockets than Hellfires were fired during the 1991 conflict.

The Hydra 70 family consists of any warhead fitted with a Mk66 rocket motor. This replaced the earlier Mk40 and provided increased velocity and spin to improve trajectory and stability in flight for better accuracy. Fitted with a warhead, the Mk66 rocket is 106cm long. After launch it reaches a velocity of 2,425ft per second before the motor burns out at 397m from the launch aircraft. The rocket spins at nine to 10 revolutions per second. Its maximum range is 10,425m compared with 8,080m for the Mk40.

Mk66 rockets were first developed by the US Army's Redstone arsenal and the various components, warheads, pods and rocket motors are produced by a variety of companies as a result of the Pentagon's second-source procurement system. In recent years Lockheed Martin Ordnance Systems, Alliant Techsystems and BEI Defence Systems have been involved in Hydra 70 contracts. For the past three years General Dynamics has been the general contractor to the US Army's industrial operations command at Rock Island, Illinois. CMS Inc produces rocket motors for the Hydra 70. Thiokol Propulsion's Cordant Technologies has developed a low-cost replacement for the Mk66 rocket that has a composite case. The rockets are to be tested and qualified from US Army Apaches during the year to prove the company's claims of increased speed and range. General Dynamics won a tightly fought contract in late 1998 to supply the Hydra 70 system for the German Army's Eurocopter Tiger attack helicopter.

Normally AH-64As fly with a pair of 19-round M261 pods carried on either in-board or outboard pylons, although seven-round M260 pods are available. In most scenarios most Apache pilots fly with a mix of rockets and Hellfire to increase their attack options. A wide range of warhead options is available to the Apache. The basic configuration involves the use of the M151 high-explosive warhead that is known as the 10-pounder to Apache crews. It has a burst radius of 10m with fragments lethal up to 50m.

For training purposes the M274 smoke signature round is employed because it has the same ballistic characteristics as the M151. It carries a potassium perchlorate/aluminium powder charge to provide flash, bang and smoke during training missions. Although no longer in production, the M229 warhead or 17-pounder, features a shaped charge warhead made of B4 composition high explosive. It remains in US Army war stocks.

Submunitions


An AH-64D Apache prototype launches a 2.75 inch rocket during field tests

The biggest boost to the Apache rocket came with the introduction of the M261 high- explosive multi-purpose submunition (MPSM) that was specifically designed for use against light armoured vehicles. It has an M439 fuse, programmable to detonate between 1,640ft and 22,966ft, along with nine M73 submunitions. The M73s are dispensed approximately 492ft above the target. Each bomblet contains a 3.2oz shaped charge to penetrate armour. The submunition then explodes into approximately 195 fragments, each travelling at 16,404ft per second. An M73 can penetrate up to four inches of armour. If detonated at an altitude of 1,000m, a single M261 warhead has a beaten zone or death zone of 56m by 17m. To simulate the M261, the US Army has fielded the M267 Smoke Signature round that uses three M75 practice submunitions with small pyrotechnic charges.

For anti-personnel or anti-soft target work the M255E1 warhead contains 1,180 hardened steel flechettes that literally fill the sky around a target with hot and sharp metal. For this reason the US Army also regards the M255E1 as an anti-helicopter weapon.

The M156 white phosphorus or smoke round is used for target marking and incendiary purposes. The M257 illumination warhead provides one million candle power over a square kilometre for at least 100 seconds, until the parachute-employed round hits the ground.

Employment of rockets can be at the hover, in level flight or diving. Hover employment is not considered optimum because the pilot may not be able to see over the aircraft's nose in some circumstances. A combination of gun and rocket fire is recommended, with rockets being used to soften up defences at 5,000m- plus ranges before the Apache closes for the kill with its 30mm chain gun. Fire control systems are now more advanced than those used in Vietnam and are fully integrated with the Apache's sophisticated night vision and targeting system. In the Gulf War US Army Apache crew fired more than 3,700 Hydra 70 family rockets using a variety of warhead combinations.

In its review of the Apache's effectiveness in the conflict, the US General Accounting Office praised the effectiveness of the rocket. It said they were used against ground targets such as aircraft on the ground, troops, personnel carriers, ammunition storage areas, fuel tanks and radar equipment. The performance of some models of the rocket was better than others, according to Apache personnel who spoke to the GAO team. The MPSM enjoyed a high success rate and one Apache battalion commander recommended that the US Army buy only that version of the Mk 66 rocket.