Insensitive Munition

BAE Systems Shoots for Stability

Courtesy: Matthew Poletti, Military Periscope

(Printed 11/25/2013) 

The military applications of explosives have been around for millennia, often traced to the Chinese invention of black powder around the 9th century. The effects of explosives introduced a new dimension to warfare.

Jumping ahead, a new industry was set off with the invention of the safety fuse and the discovery of nitroglycerine in the 19th century. Trinitrotoluene (TNT) was invented in 1863 and dynamite was patented in 1867. More powerful RDX, HMX and other explosive chemicals followed in the 20th century.

These advances were accompanied by the inherent dangers to those employing explosives. (Emile Nobel -- the brother of Alfred Nobel, who patented dynamite -- was killed by nitroglycerine.) The object is to control the explosion, not to have it go off when you least expect it to do so.

The USS Forrestal during the Vietnam War offers a major case in point.

On July 29, 1967, that American supercarrier was in the Gulf of Tonkin. A power surge accidentally launched an unguided Zuni rocket from an F-4B Phantom II that was preparing to launch. The rocket struck a wing-mounted external fuel tank on a nearby A-4E Skyhawk, igniting a fire that began to consume World War II-era, 1,000-lb AN-M65 bombs on the deck. The bombs were made with Composition B, a TNT/RDX mixture with the unfortunate tendency of becoming more powerful and sensitive as it ages.

In about a minute, an AN-M65 exploded, killing the carrier's on-deck firefighting crew and blowing a crater in the deck. A chain reaction of blasts and a massive fire claimed the lives of 134 men and injured 161 others before being brought under control the next day. Twenty-one aircraft had to be stricken from naval inventory.

The Forrestal fire was so devastating that the Navy still looks to the lessons learned from that accident when teaching damage control and munitions safety. 

Combining Capability and Reliability

That deadly accident highlights the importance of insensitive munitions (IMs), which are designed not to explode when exposed to impact, heat or friction. Officials from the Ordnance Systems sector at BAE Systems discussed the IM effort with Military Periscope at the Association of the U.S. Army (AUSA) exhibition, held last month in Washington, D.C.

The U.S. military was actually working on such explosives by the time of the Forrestal fire. The new Mark 83 1,000-lb bomb was built with Composition H6, a mixture of RDX, TNT and other materials that could survive 10 minutes in a jet fuel fire without cooking off. The unstable AN-M65s were only called into service because of a critical shortage of 1,000-lb bombs.

It was not until the late 1990s, however, that the Dept. of Defense significantly expanded its government funded IM research -- sparked in part by another munitions accident. A fire at Camp Doha, Kuwait, on July 11, 1991, set off 155-mm artillery shells. That, in turn, triggered an hours-long series of explosions that damaged or destroyed 102 Army vehicles. Forty-nine U.S. Army soldiers and four British personnel were injured.

The Pentagon came to attention over energetic materials -- the collective name for explosives, propellants, pyrotechnics and their ingredients.

The Holston Army Ammunition Plant in Tennessee is a DoD facility. It has been run by BAE since 1999and is at the forefront of the IM effort. Several products involving insensitive munitions developed at that facility have been fielded for use in warheads, bombs, mortars, artillery, fuzes, grenades and submunitions, according to Michael Ervin, director of research and development at BAE's Ordnance Systems.

BAE was also awarded a contract in 2012 to run the Radford Army Ammunition Plant in Virginia, a site focusing on the manufacture of propellants for weapons systems. These products include IM variants that are still under development.

These efforts have resulted in the IMX next-generation family of melt-pour insensitive munitions. They are able to survive bullet impacts, sympathetic detonation and even a shaped-charge jet impact without exploding. A strike by a rocket-propelled grenade (RPG) is an example of the latter.

In 2010, the U.S. Army first approved IMX-101 as a replacement for TNT in artillery and other large caliber munitions. It was the only product to pass all of the Army's safety criteria, including an RPG strike. Time magazine dubbed it one of the 50 greatest inventions of the year, and more awards have followed.

IMX-101 entered into full production this year at Holston. In March, the Pentagon awarded BAE an $18.4 million order for the IM replacement for TNT. The total award to run Holston, including the IMX-101 portion and plant management, runs through the end of September 2017. That could be worth up to $781 million.

The insensitive product is used in the IM M795 155-mm artillery round as a replacement for TNT-based munitions. That artillery round is typically fired from the M777 howitzer, also made by BAE and used by U.S. and allied forces worldwide.

On deck is another explosive mixture: IMX-104. BAE manufactures that at Holston as a replacement for Comp B in 60-mm, 81-mm and 120-mm mortar rounds. IMX-104 is in the process of being qualified by the Army, Ervin told Military Periscope. BAE also works at Holston with the PAX family of IMs and aluminized versions of the IMX products. 

Measuring Costs, Benefits

IMX-101 and IMX-104 have undergone accelerated aging testing prior to being qualified, as we were told by James Chang, Anthony Di Stasio and Philip Samuels, members of the Explosives Development Branch at the Army Research Development and Engineering Center (ARDEC) at Picatinny Arsenal, N.J. The IMX family of explosives is expected to age just as well as the current munitions stockpile, with a shelf life of 20 years.

As always, cost matters. How does the price of IMX-101, for instance, stack up to TNT? When reporting on IMX-101 in 2010, Time noted that the product cost US$8 per pound, compared to $6 for a pound of TNT. The Army acknowledges that a new material is typically expected to cost more at first.

In the case of IMX, the price tag is affected by numerous factors, including the smaller quantity being procured, a different manufacturing process and new constituents in the formulation. The increase is likely to be mitigated eventually.

For example, the storage, transport and handling of IM materials are projected to be cheaper over the life of the product. Since the munitions are less vulnerable to accidental detonation, IMX can be packed more tightly in storage. This is expected to recover most, if not all, of the higher material costs, according to the Army.

As the military continues making the transition to IMX-101 and IMX-104, the amount procured will increase and the unit cost will go down. The Navy and the Air Force are already evaluating the use of aluminized IMX-101 in 500-lb Mark 82 general-purpose bombs. If it is adopted, that would double the amount of IMX-101 in use by the United States and drive the cost below that of TNT.

The IMX family is also produced in the United States; TNT is not.

A strict dollars-and-cents analysis does not take into account the incalculable: the potential lives and materiel saved by adopting insensitive munitions.

The process of replacing TNT and Comp B with IMX is seen in the Pentagon as one of the greatest successes in military science in the last 50 years, ARDEC officials told Military Periscope. The ultimate goal is to field IM-based systems -- both explosives and propellants -- across the entire U.S. military. IMX-101 and IMX-104 were the Army's first priorities because artillery and mortars use so many munitions.

Once IMX-101 and IMX-104 are fully implemented with these weapons, an evaluation will be made on their potential use in other TNT- or Comp B-based munitions. The Army is considering the fielding of insensitive munitions across its entire portfolio, from 25-mm rounds up to 250-mm rockets.

Naturally, there are challenges. The Pentagon has not implemented new energetics on this scale in decades. Emerging environmental and occupational safety standards have also presented hurdles.

Meanwhile, many of the raw materials used in munitions are at risk of becoming unavailable to the Pentagon over the next couple of years, according to a team chartered early last year for the undersecretary of Defense for Acquisition, Technology and Logistics. This could mean that in certain instances the DoD would have to rely on foreign suppliers.

Both defense researchers and private-sector officials are confident the obstacles can be overcome -- producing munitions that minimize the risks to American troops while providing the Army with plenty of bang for its bucks.

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Allie Rogers
Specialist, Communications
Combat Mission Systems / Ordnance Systems Inc.

Office: +1 423-578-6394
Mobile: +1 423-444-3246

12 Default Profile Image
Allie Rogers
Specialist, Communications
Combat Mission Systems / Ordnance Systems Inc.

Office: +1 423-578-6394
Mobile: +1 423-444-3246