Despite all the precautions during design and operation of magazines, accidents do take place with ammunition, which lead to terrible outcomes on warships and loss of precious lives. A need was therefore felt to make explosives inherently less sensitive so that they remain passive to external stimuli like heat, shock, bullet or fragment impact and sympathetic detonation in case nearby munitions function.
Safety of ammunition and explosives onboard is of paramount importance for the survival of the warship. There are two aspects which merit attention in this regard; one pertains to the safety and prevention of fire during storage of these potentially hazardous items and the other to making the explosive devices safe for storage by improving their compositions.
Stowage of Ammunition and Explosives on Board
A warship takes onboard only that ammunition which has been certified fit for use by the armament inspection agency. Stowage of ammunition and explosives onboard is a complex design exercise due to space constraints, positioning of adjacent equipment compartments depending upon hazards posed, ease of weapon handling, positioning of ammunition delivery mechanisms, minimising damage, ease of firefighting and so on. The problem is further complicated as the stowage has to be secure against roll, pitch and yaw motions of the ship, extremely high humidity levels and various intensities of storms. There are explicit design guidelines, which are refined periodically for safety enhancement. As for the ammunition, its remaining operational life is calculated depending upon the levels of environmental stresses experienced by it during its storage onboard as well as the prevalent shock and vibration levels of a particular type of ship.
There are different types of stowage spaces for different types of ammunition and explosives and they are stored in separate lockers or magazines. The lockers and magazines are clearly marked indicating the type of explosives, its fire safety hazard and the permissible quantity in that space. The warnings on stowage spaces are prominent and visually indicative leaving no doubts in the minds of personnel entering the area.
There are various types of magazines namely primary, missile, ready to use magazines and lockers. Primary magazines are generally located below the waterline and are equipped with temperature control, heat insulators and adequate means of ventilation. Missiles magazines are a special category since missiles are largely integrated in nature i.e. the safety and arming mechanism is pre-assembled to the warhead, which in turn is connected to the electronics and the rocket propellant, thus raising its hazard level. Further, they are housed in special casings, boxes or canisters and stored separately. The handling equipment to bring them to the launcher could be operated by a combination of electric-pneumatic and/or hydraulic systems. Extreme care is required during handling as the rocket propellant may ignite in case the missile falls and thereby launches the missile in a confined space causing havoc. Ready to use magazines are located near the weapon for which they are intended. Those are also well ventilated, insulated from heat and fitted with sprinklers. Ammunition lockers are used to store special types of explosives and ammunition such as detonators and pyrotechnics. The lockers are secured to the deck of the ship and it is ensured that ammunition inside does not move or rattle about during routine motion of the ship at sea.
Single purpose magazines are those which store a single type of explosive store for e.g. Rocket motor magazine, small arms magazine, fixed ammunition magazine, missile magazine, fuse magazine, detonator locker, pyrotechnic locker and so on. Mixed explosive storages are also permissible in certain combinations of explosive stores depending upon the severity of explosive sensitivity. It is ensured however that the ammunition stored onboard is as per regulations and within permissible limits.
Environmental control of magazines: Magazines are fitted with safety and environment control features, so that the ammunition and explosives remain protected from excessive humidity and temperature. Ventilation and exhaust systems are installed in the magazines and they are regularly vented to evacuate accumulated toxic gases if any. Missile magazines are vented to the atmosphere for the simple reason that in case a missile rocket motor functions, its exhaust is immediately vented to the atmosphere before it can spread to other areas.
Sprinklers and alarms: Largely, all types of magazines have sprinkler systems fitted in such a way that water is sprayed on to the ammunition and explosives and the entire magazine is flooded in case of smoke/fire detection or rapid rise in temperature. These can be operated automatically by remote control or manually. Ammunition, which functions by ingress of water, is not stored in such magazines. The alarm system comprises of alarms that operate on detection of high temperature, activation of sprinklers and functioning of flooding systems.
Inspections: Magazine inspections are carried out by qualified sailors and recorded in inspection logs. Daily inspection involves ensuring that ammunition is properly secured, the magazine is clean, there is no presence of fumes or odour and that there is nothing out of the ordinary in and around the magazine. Special attention is paid to the fact that there should be no hindrances in entry and exit to the magazine, abnormality in rise of temperature and humidity charts, unnatural accumulation of material in and around the area, etc. In addition, the magazine and surrounding area is inspected for leakages or breakages in sprinkler systems, functioning of alarm systems and abnormal heating in adjacent compartments. Each magazine is monitored for temperature and humidity and records of maximum and minimum values are entered in the magazine’s log card inside the magazine. The magazines are inspected prior to locking and remain locked when no activity is being carried out and only authorised personnel can access them.
Movement of ammunition: Shifting of ammunition for routine firing exercises, rearrangement or during ammunitioning/ deammunitioning are inherently dangerous activities where the slightest mistake can lead to catastrophic situations. Therefore, utmost care is exercised during such work. Explicit orders are available for each activity and it is ensured that the orders are complied with at all times. Ammunitioning and deammunitioning is carried out at designated jetties or explosive anchorages so that in case of any accident, the damage is limited to that ship only. Transfer of ammunition at sea is carried out only in exceptional circumstances as it is a very dangerous activity. Detailed orders are prepared by both ships and preparations checked and rechecked prior to carrying out this operation. The ships remain in highest degree of nuclear, chemical and biological damage control readiness during the process.
Despite all the precautions during design and operation of magazines, accidents do take place with ammunition, which lead to terrible outcomes on warships and loss of precious lives. The men onboard a warship work and sleep virtually next to the magazines, accidental fires in other areas may also lead to explosions or large fires in magazines due to cook off or other causes. A need was therefore felt to make explosives inherently less sensitive so that they remain passive to external stimuli like heat, shock, bullet or fragment impact and sympathetic detonation in case nearby munitions function. The genesis of the thrust in insensitive ammunition development lay in two major accidents in the US, namely the 1966 Palomares B-52 Crash and the 1968 Thule Air Base B-52 Crash in which the high explosive devices used in the nuclear bombs had detonated on impact. The US Navy too has witnessed many accidents in the 1960s. In 1966, there was a fire onboard USS Oriskany due to mishandling of an aircraft flare, which led to detonation of 2.75 rocket warheads and resulted in the death of 44 sailors. In 1967, a five-inch Zuni rocket loaded on the pod of an F-4 aircraft onboard USS Forrestal was accidentally fired, which in turn led to fires and functioning of several bombs, rockets and missiles. The disaster resulted in deaths of 134 personnel. In 1969, onboard USS Enterprise, the exhaust from an aircraft engine starter unit caused detonation of five-inch Zuni rockets, whose warheads were filled with composition B explosives. This resulted in 18 warhead explosions and 28 deaths. In December, the same year, ammunition ship SS Badger encountered rough seas during a storm due to which the bombs broke loose from the pallets and led to explosions as they were tossed around the deck. The ship had to be abandoned and 26 lives were lost. In addition, the US Navy experienced 16 premature explosions of shells of high calibre guns during the period December 1968 and January 1973. The shells were either filled with Composition A-3, Composition B or explosive D. The incident onboard USS Newport on October 1, 1972, deserves mention, in which the projectile of eight-inch ‘bag gun’ detonated in ram position in the gun chamber. In the explosion and ensuing fire, 20 sailors died. Compositions of the type mentioned above are prone to ignition when subjected to adiabatic heating during operation/acceleration of projectile in the gun barrel. The above incidents and similar ones in the Army depots provided impetus to research on insensitive munitions.
Conceptually insensitive munitions should not explode but only burn when subjected to slow and fast heating, hits by bullets, shrapnel or shaped charges. Research is being progressed adopting approaches, like externally protecting the explosive device during transportation by incorporating thermal insulation and venting, and by improving explosive compositions to provide high stability. Insensitive munitions contain shock and fire resistant ‘insensitive high explosive’ like plastic/polymer bonded explosives or triaminotrinitrobenzene (TATB). TATB’s shock and thermal stabilities are higher than that of any other comparable material. Further it is reasonably powerful high explosive thus favouring its induction in munitions. Some of the newer compositions are insensitive munitions explosive IMX-101 (consisting of 2, 4-dinitroanisole and nitrotriazalone amongst others, developed by BAE Systems and cleared for use by the US Army) and FOX-7 (1, 1-diamino-2, 2-dinitroethene (DADNE) of Sweden).
With an order from France to develop and qualify modern naval ammunition, Diehl Defence has become the first supplier worldwide of naval ammunition, meeting the requirements of insensitive ammunition (IM). It constitutes a refinement of the 76mm naval ammunition employed worldwide. The new ammunition, a joint cooperation of Diehl Defence and the French manufacturer Nexter Munitions, is being realised with insensitive explosives and is scheduled for deployment in the Oto Melara SUPER RAPIDO L-62 naval guns of the new frigates FREMM and HORIZON from 2015. The 76mm ammunition is capable of engaging both air and sea targets as well as coastal targets.
A major opposition to use of insensitive munitions has been the view that the explosive power of these is inferior to the ones filled with TNT/HMX. However, this objection is more than offset by high accuracy of new delivery systems wherein much fewer munitions are required to achieve the same impact on target. During Operation Desert Storm, laser guided bombs accounted for about ˜50 per cent of destroyed targets, despite the fact that their numbers were less than five per cent of the total ordnance fired. The navies across the globe are today committed to the use of insensitive munitions and are gradually replacing the TNT/RDX/HMX compositions. This is not to say that completely insensitive munitions have been developed and available for use by the armed forces or that all the requirements of insensitive munitions are met prior to its induction. Incremental improvements are being accepted as they are helping in reducing the risks and increasing survivability at sea as compared to the older explosives. As an example PBXN-109 meets all requirements except that of sympathetic detonation and hence has been inducted in bombs and missile warheads since the older filling had not met even a single insensitive munitions criterion. The UK Ordnance Board Proceeding 42657 commenting upon usefulness of insensitive munitions has stated:
Many North Atlantic Treaty Organisation (NATO) countries and other allies of the US are supporting the insensitive munitions programme. As far as indigenous developments are concerned, the High Energy Materials Research Laboratory of The Defence Research and Development Organisation (DRDO) claims to have developed 12 compositions in the insensitive munitions category along with CL-20, the world’s ‘most powerful’ non-nuclear explosive. These would find applications in warheads, rockets or gun propellants. Laboratory production of these has also been established.
In conclusion it can thus be seen that navies are very conscious and proactive about structural safety of magazines, safety procedures during handling as also researching into sensitivity reduction of explosives to ensure enhanced safety of men and material onboard warships.
The author is former DG NAI and Senior Fellow at New Westminster College, Canada