There has been significant progress made toward meeting the U.S. Navy’s IM goals. Today, all new U.S. Navy warheads are being loaded with PBX’s. These new compositions are less likely to detonate in aircraft fuel or other fires and are relatively insensitive to bullet and fragment attack
PBXN-7, a new booster explosive comprised of TATB, RDX, and a plastic binder has essentially solved the booster cook-off problem as was experienced on the USS NIMITZ on 26 May 1981. As mentioned above, the fire on the flight deck of the NIMITZ had been extinguished when the booster explosive in a SPARROW missile warhead detonated.
New energetic molecules like CL-20 (hexanitrohexaza-isowurtzitane), ADN (ammonium dinitramide), and ADNBF (7-amino-4,6-dinitrobenzofuroxan) have been synthesized and show promise in powerful, insensitive, environmentally friendly compositions. New explosive compositions based on NTO (3-nitro-1,2,4-triazol-5-one) are expected to meet all the IM requirements. The NTO compositions are in the advanced stages of development and may soon be available.
The IMAD Propulsion Technology program has made substantial progress in reducing the sensitivity of rocket motors and limiting the severity of reactions when they occur. Reduced smoke propellants based on small particle size ammonium nitrate or CL-20 are in advanced stages of development and are expected to meet the IM requirements.
Filament wound, strip laminate and hybrid case designs and Preferential Insulation Techniques (PIT) are some of the techniques used that allow the rocket motor case to weaken and reaction products to vent non-explosively are becoming available commercially. For PIT, external insulation is applied to the rocket motor to delay the cook-off reaction. Then a narrow strip of insulation is removed along the length of the case. Upon rapid heating, the unprotected metal in the strip weakens and ruptures as the internal pressure rises. This allows the gases to vent. PIT applied to rocket motors has been shown to markedly reduce the violence of the cook-off reaction
The third technical area addressed by the IMAD program is Ordnance Technology. This part of the IMAD program focuses on warhead designs, reaction barriers, weapon containers, warhead booster designs and development and maintenance of an IM database.
Machining a stress riser grove along the length of the heavy metal case is one method that can be used to reduce the severity of the warhead cook-off reaction. In a fire, the internal pressure resulting from decomposition of some of the explosive charge ruptures the case along the grove. This allows the case to vent before the explosive reaches a critical pressure where a violent reaction with fragment projection could result.
Considering the improvements realized it is difficult to understand the rational for the lack of interest in the IM concept by some of the weapons program offices. IM is cheap compared to the alternatives. Even if we neglect the needless loss of life in accidents, munitions are vulnerable to enemy action and sabotage. If the operators do not support the IM concept, the logisticians should. A recent article addressed the logistics concern as follows:
“Ammunition presents a number of logistic challenges, both on and off the battlefield, that bear directly on the current state of affairs. First, it is explosive. From numerous catastrophic ammunition accidents, we know that there can be no relaxation of the safety rules in combat without great risk. This characteristic of ammunition is even more troublesome for the logistician. Stockpiles are vulnerable to loss through enemy action, deliberate sabotage or direct combat, and inadvertently, through carelessness. The high probability of these events occurring in combat must be considered by the planner when determining ammunition requirements.” 90
On 4 November 1994, the Office of the Under Secretary of Defense, Acquisition and Technology reemphasized the strong DoD support for the Joint Service Insensitive Munitions policy. In an attempt to resolve an issue among the Services on how best to address the IM goal the Undersecretary sent a memorandum to the Chairman of the Joint Requirements Oversight Council stating the following:91
“The development and production of insensitive munitions (IM) has been a goal of the Department for almost ten years now. But there is disagreement within the acquisition management community on how to best achieve that goal.
In 1987, the Secretaries of the Military Departments signed a joint Memorandum of Agreement that stated, in part, ‘to the extent practical, all munitions should be made to meet IM criteria.’ Despite this agreement, there has been continuing concern about whether implementation has been as rigorous and comprehensive as should be. To address this concern, the Joint Ordnance Commanders Group in 1992 developed an IM policy statement intended for publication in DoD Instruction 5000.2.
… A basic underpinning of this argument is that the increasing emphasis on joint military operations, as evidenced in Operation Desert Storm and Haiti, puts a great premium on interoperability and safety, precisely the concerns that the design and production of IM-qualified munitions are supposed to address. Thus, a statement requiring IM factors to be considered in the acquisition process is appropriate.
However, the Army and the Air Force have taken issue with this approach. Their essential argument is that IM technical specifications are driven by requirements, not by acquisition policy…
…I would like to obtain the official Joint Requirements Oversight Council (JROC) position on IM. Do you agree that the best way to address the Departmental goal of meeting operational requirements with the least sensitive system design available is through the requirements process? Or, do you think that the Department’s objectives would be better served by an acquisition policy statement? Finally, if we were to address this issue through the requirements process, is there a mechanism to ensure that IM is routinely considered? I look forward to the JROC position…”
From this memo, it appears that the DoD was willing to force the issue by either including the Joint IM policy statement in DoD Instruction 5000.2, the acquisition document, or require a formal documented procedure to assure that the policy is routinely considered in the munitions requirements process.
Other DoD Directives followed. The policy statement was added to follow-on editions of DoD Instruction 5000.2 and a Tri-Service Product Team was established to review IM compliance efforts and provide recommendations to the Service Authorities. As shown by Annex 3, the concept has progressed, gradually, and has now become an established requirement culminating in the issuance of a Joint Requirements Oversight Council Memorandum92 that states:
“Effective immediately, all munitions systems will incorporate insensitive munitions (IM) as a required certification in their capabilities documents…”
90Greenberg, Paul L., “Shrinking U.S. Stockpile Risks Nation’s Security”, National Defense, P. 36, May/June 1995.
91OUSD(Acquisition & Technology) Memorandum to the Chairman, Joint Requirements Oversight Council dated 4 November 1994.
92Joint Requirements Oversight Council Memorandum JROCM 113-04 of 2 July 2004