Third revision of the Navy Insensitive Munitions Policy and the U.S. military standard defining the Insensitive Munitions Requirements

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The third and final revision of the Navy Insensitive Munitions policy was issued by Adm. Frank B. Kelso II on 18 February 1993.83 It was issued, mostly, to reflect the new OPNAV organization and assure maximum compliance with the provisions of the Insensitive Munitions Joint Memorandum of Agreement signed by the Service Secretaries in 1987.

This third revision of the IM policy assigned NAVSEA the responsibility of coordinating the U.S. participation in the NATO Insensitive Munitions Information Center, NIMIC, in Brussels Belgium. Also, the previous instructions had stated that the Navy’s policy was to be considered in all dealings with other services or foreign military agencies. The revised instruction defined this further as follows:

“The Navy’s IM policy extends to all munitions regardless of the source of design or manufacturer which are used, stored or transported aboard U. S. Navy ships, weapon platforms, weapon carriers, and munitions held at Navy shore activities. Every effort shall be made with other services to ensure maximum compliance with the provisions of reference (a), the Insensitive Munitions Joint Memorandum of Agreement.”

As mentioned above, MIL-STD-2105A (Navy) was published on 8 March 1991.84 It was intended to be a tri-Service document and, as such, was staffed in the three Services and the Marine Corps. Difficulty in obtaining Army and Air Force agreement delayed the publication. As an interim measure, the standard was issued as a Navy document and the Army issued a supplement for its use pending resolution of the problems. Like its predecessor, the standard presented a compendium of the basic tests required to assess explosive safety in munitions. But in addition, it defined the insensitive munitions tests and identified passing criteria for each test.

MIL-STD-2105A made the following changes to the IM requirements:

  1. The bullet impact test was changed from a single impact with a 20 mm projectile at service velocity to three .50 caliber armor piercing projectiles impacting the test item at 2,800 +200 ft/sec.
  2. It required the performance of a fragment impact test. The test described consisted of striking the item with three to five one-half inch, 250 grain, mild steel cubes traveling at 8300 +300 ft/sec.
  3. It required a sympathetic detonation trial with the test set-up based on a threat hazard analysis.
  4. To satisfy Army requirements, optional tests for shaped charge jet impact and spall were included. The requirement for conducting these tests was based on their applicability as determined by a threat hazard analysis.

The Joint Service standard, MIL-STD-2105B, was issued on 12 January 1994.85 The Propulsion (Type VI) reaction was deleted from the definition of test results. All of the other definitions in the previous standard used for describing the reactions that could occur in the IM tests remained the same. Also, the Fast Cook-Off, Slow Cook-Off, and Spall test requirements remained the same. The Bullet, Fragment, and Shaped Charge Jet Impact tests were changed to be consistent with the Army Supplement to MIL-STD-2105A(Navy).

The new tri-Service bullet impact test required that, based on a threat hazard assessment, the munition be hit “by one to three .50 caliber type M2 armor-piercing (AP) projectiles. The projectiles were aimed at a common point and were projected at a velocity of 850 +60 m/s (2,800 +200 ft/s). An 80 +40 milliseconds firing interval was specified.

Two bullet impact trials were required. In one trial, the impacting projectiles were to penetrate “the most sensitive material(s) that were not separated from the main explosive charge by barriers or other safety devices”. For the other trial, the bullets were aimed at “the most shock-sensitive location (typically the ignition/initiation system)” of the item.
For fragment impact, the revised standard provided a preferred and an alternative test. The preferred test was the same as that documented in MIL-STD-2105A. The alternate fragment impact test procedure provided in the new standard was to use a single mild steel conical shaped fragment traveling at a velocity of 6,000 +200 ft/s (2,530 +60 m/s). The Navy generally uses the preferred test as their IM requirement.

The Joint Service standard also provided a preferred and an alternative test for the shaped charge jet impact tests. The preferred test used the same 50 mm Rockeye-type shaped charge as specified in MIL-STD-2105A. The alternate test method was not specific. It specified that the test set-up, shaped charge, and passing criteria would be designed and selected based on the threat hazard assessment.

On 30 June 1994, RAdm. Rempt, N865, as the OPNAV sponsor reemphasized the importance of the Insensitive Munitions Advanced Development program and set priorities for the work performed in that effort. In his letter he stated the following:86

” The IMAD technology priority development efforts should continue to stress application to: 1) new weapons in development, 2) weapons with established product improvement programs, and 3) weapons in the existing inventory. The policy of the IM Council … will remain that of integrating all available technology into new development and P3I weapons to achieve IM compliance….

The IMAD projects should continue with efforts in explosives, propulsion, and ordnance technology…. the Resource Sponsor directs that major emphasis, and first priority of effort, be on high performance rocket propulsion. The areas of sympathetic detonation resistant explosives, and innovative warhead design concepts should continue to be pursued as second and third priority…..”.

The priorities assigned by the RAdm. Rempt letter reflected the realization that there had been significant progress made in the IMAD explosives and warhead technology areas. However, major sensitivity problems still existed with large rocket motors. In general, the mass of propellant in the rocket motor exceeded by far the mass of high explosive in the warhead. Also, work on producing less sensitive high explosives started some 15 years before there was any work devoted to desensitizing rocket motors. After all, it was during the Insensitive Munitions CEB briefing preparation that the sensitivity problem with high-energy propellants was finally acknowledged.

The assessment methodology used by NAVSEA to assign IM certification begins with the assignment of the munition to one of two categories, “Ship Killer” or “Non-Ship Killer”.87 Ship Killers are defined as munitions having the potential to cause significant damage to ships in excess of the damage that would be inflicted by the IM stimulus alone and would probably cause the ship to abort its mission and return to port for repairs. The fifteen munitions on the IM Council’s priority list are acknowledged ship killers.

Non-ship killers are munitions, which would not cause significant collateral damage to ships in excess of the damage inflicted by the IM stimulus. The ship could no doubt continue on its mission. Examples of “Non-Ship Killers” are flares, cartridge activated devices, 20 mm Ammunition, smokes, etc.

The predictive methods used for the IM assessments are based on sensitivity data for the energetic materials. The data are obtained from small scale laboratory tests, generic hardware tests, large scale munition tests, hazard classifications tests, engineering analyses by knowledgeable persons, and computer mathematical modeling.

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83OPNAVINST 8010.13C, N865, Department of the Navy’s Policy on Insensitive Munitions (IM), dated 18 February 1993.
84MIL-STD-2105A(NAVY), Hazard Assessment Tests for Non-Nuclear Munitions, AMSC N6037, dated 8 March 1991.
85MIL-STD-2105B, Hazard Assessment Tests for Non-Nuclear Munitions, AMSC N6037, dated 12 January 1994.
86OPNAV ltr. Ser. N865/4U65285C dated 30 June 1994; Subj: Insensitive Munitions Advanced Development Program.
87Bowen, Richard E., Presentation to the IMAD Advisory Group, Arlington, VA, 17 March 1994.