HMX was discovered as a by-product in the production of RDX. Although it is almost as sensitive and powerful as RDX, it is seldom used alone in military applications but is normally mixed with another compound, such as TNT. In the Navy, HMX is used as an ingredient in plastic-bonded explosives.

RDX (Cyclotrimethylene Trinitramine)

RDX, also known as Cyclonite or Hexogen, is considered the most powerfid and brisant of the military high explosives. It is also one of the most used high explosives in Navy munitions.

RDX is a white crystalline solid that has a high degree of stability in stowage. It is usually used in mixtures with other explosives, desensitizers, or plasticizers. The most used compositions of RDX are included in the following paragraphs.

COMPOSITION A-3.- Composition A-3 is a wax-coated, granular explosive, consisting of 91% RDX and 9% desensitizing wax.

Composition A-3 is not melted or cast. It is pressed into projectiles. It is nonhygroscopic and possesses satisfactory stowage properties. Composition A-3 is appreciably more brisant and powerful than TNT; its velocity of detonation is approximately 27,000 fps. It may be white or buff, depending upon the color of the wax used to coat the powdered RDX.

Composition A-3 is used as a fillerinprojectiles that contain a small burster cavity, such as antiaircraft projectiles. It can be used as compressed fillers for medium-caliber projectiles.

COMPOSITION B.- Composition B is a mixture of 59% RDX, 40% TNT, and 1% wax. The TNT reduces the sensitivity of the RDX to a safe degree and, because of its melting point, allows the material to be cast-loaded.

The blast energy of Composition B is slightly higher than that of TNT. Composition B is nonhygroscopic and remains stable in stowage. It has an extremely high-shaped-charge efficiency. The velocity of detonation is approximately 24,000 fps, and its color ranges from yellow to brown.

Composition B has been used as a more powerful replacement for TNT in loading some of the rifle grenades and some rocket heads. It can be used where an explosive with more power and brisance is of tactical advantage and there is no objection to a slight increase of sensitivity.

While no longer used in newer gun projectiles, some older stocks may be found with Composition B main charges.

COMPOSITION C.- Compositior C-3 is one of the Composition C series that has now been replaced by C-4, especially for loading shaped charges. However, quantities of Composition C-1 and Composition C-2 may be found in the field. Composition C-1 is 88.3% RDX and 11.7% plasticizing oil. Composition C-3 is 77% RDX, 3% tetryl, 4% TNT, 1% NC, 5% MNT (mononitrotoluol), and 10% DNT (dinitrotoluol). The last two compounds, while they are explosives, are oily liquids and plasticize the mixture. The essential difference between Composition C-3 and Composition C-2 is the substitution of 3% tetryl for 3% RDX, which improves the plastic qualities. The changes were made in an effort to obtain a plastic, puttylike composition to meet the requirements of an ideal explosive for molded and shaped charges that will maintain its plasticity over a wide range of temperatures and not exude oil.

Composition C-3 is about 1.35 times as powerful as TNT. The melting point of Composition C-3 is 68C, and it is soluble in acetone. The velocity of detonation is approximate y 26,000 fps. Its color is light brown.

As with Composition B, Composition C is no longer being used as a gun projectile main charge. However, some stocks may still be in service with Composition C-3 used as a main charge.

Explosive D

Explosive D (ammonium picrate) is a yellow crystalline material. It is less sensitive than TNT or Composition A-3 and is generally used in projectiles that must penetrate hard targets, such as armor, without detonating.

Plastic-Bonded Explosives (PBXs)

PBXs are relatively new types of explosive compositions that have found increased use in naval weapons. They are generally made of an explosive

compound like RDX or HMX incorporated into either an energetic or inert plastic binder.

PBXN-5

PBXN-5 is referred to as a plastic-bonded explosive because it is an explosive coated with plastic material. The composition is made of 95% HMX and 5% fluoroelastomers.

PBXN-106

This explosive is one of the new plastic-bonded explosives. It is a cast-cured explosive composition made from a homogeneous mixture of RDX in a plasticized polyurethane rubber matrix. Once cured, the material cannot be easily restored to a liquid state. The finished material is flexible and will absorb considerably more mechanical shock than conventional cast or pressed explosives.