American Projectiles and Explosives
Introduction to American High Explosives
The information that will follow in the following weeks and months is, like with other inventories, taken from documents written at the time or soon after World War II. These were written by British or American teams in order to categorize enemy or friendly ordnance. This American inventory should be up to date to about February 1946, and was published in 1947.
Ordnance included was that classified as service, together with some obsolete, obsolescent, and experimental types. The experimental items were those being actively developed in the Spring of 1946, with the probability that they would soon be standardized.
Obsolete and obsolescent equipment described was that which might still be in existence in depots or dumps at the time of writing.
When a Navy ordnance item is approved for testing, it is assigned its Mark number. It retains this Mark number whether finally approved for service use or rejected. Modifications to the original Mark design are treated likewise. Army items under development as assigned "T" numbers. If the item is standardized by the Army's Ordnance Technical Committee, the "T" designation is dropped and an "M" number is assigned.
When a modification on a "T" item is made, the change is given an "E" number: for instance, "T1E1". If the modification is adopted as a standard item, the modification gets an "A" number in sequence of change on the standard item: for instance, "M66A1, M66A2". The Army's Chemical Warfare Service uses "E" and "R" designations for experimental items instead of the "T" and "E" numbers, respectively, of the Ordnance Department.
For aircraft ordnance there are items which are standardized for both the Navy and the Army. These are given the letters "AN" before their original standard name; thus, AN-Mk 33 or AN-M63A2.
Prior to June 1925, the Army's nomenclature for bombs was by a Mark and a Roman numeral, like the early Naval Mark designations, but the modifications were distinguished by the letter "M" and another Roman number (Mk I M II) where the Navy used the abbreviation "Mod", (Mk 1 Mod 2). In 1925, the Army adopted the "M" system. The Army-Navy Standardization Board was created in June, 1941.
American High Explosives
Two scales are employed to compare sensitivity of explosives. The first of these is the "Laborator Impact Sensitivity" in which the ratio of the drop of a given weight necessary to detonate the explosive under discussion to the drop necessary to detonate TNT, is expressed on a percentage basis. TNT will be given as 100.
The second is a scale of "Bullet Impact Sensitivity" with RDX rated at 0 and TNT at 100. The other explosives are expressed in relation to these two. Velocity of detonation varies directly with the density to which the explosive is cast or pressed, all other factors being constant. The velocity of detonation will, therefore, be given for a definite density of loading.
TNT is powerful, brisant, easy to load by casting since its melting point (Grade A) is 80.2 degrees Celsius, stable under all stowage conditions, insensitive enough to stand all normal handling, and even capable of standing bullet impact when cast. The Navy uses it as a booster in a pressed granular form in which it is more sensitive to detonator action.
The velocity of detonation is 22,300 feet/second at a density of 1.55. Its Laboratory Impact Value is 100. Its Bullet Impact Value is 100. Its color is yellow to buff.
Tetryl, because of its combination of high power, brisance, and sensitivity, is the standard US booster charge, although the Navy still uses an appreciable amount of granular TNT. It has been tried for main charge loads in small caliber projectiles, but has proved too sensitive to withstand the setback in all but 20mm. It is used as abase charge in compound detonators. This, in effect, makes it a small booster in intimate contact with the initiating explosive.
The melting point of Tetryl (130 degrees Celsius) is too high to allow it to be melted and cast. It is loaded by being mixed with small quantities of graphite or stearic acid which serve to lubricate it while it is being pressed into pellets. Tetryl is quite safe to handle and is extremely stable in stowage. Exposed or loose Tetryl should not be handled, as it may cause dermatitis.
The velocity of detonation is 24,400 feet/second at a density of 1.55. Its color is light yellow, but it is usually gray because of the graphite. It is more powerful than TNT. Its Laboratory Impact Value is 45, and its Ballistic Impact Value is 61.
Explosive D (Ammonium Picrate)
Explosive D is the standard main charge for armor-piercing bombs and projectiles and other Navy projectiles. While its power and brisance are slightly inferior to TNT, it is much more insensitive to shock and will stand impact on armor plate without being deflagrated. It has two other disadvantages: (1) Its melting point is too high for it to be melted and cast, and it is therefore loaded by being pressed into cases by a hydraulic ram; (2) It reacts with metals to form extremely sensitive compounds. This is counteracted by covering the interior of bombs or projectiles with acid-proof lacquer.
Its rate of detonation is 21,300 feet/second at a density of 1.48. Its power and brisance are about 95% those of TNT. Its Laboratory Impact Value is 99; its Bullet Impact Value is over 100. Its color is yellow or yellow-orange.
RDX (Cyclonite Cyclotrimethylenetrinitramine)
RDX is the most powerful and brisant of the military high explosives, and it is considered much too sensitive to use alone. It seems to be about half way between Tetryl and PETN in mixtures of other explosives and inerts which reduce the sensitivity to a safe range, while the mixtures have a very high brisance and power due to the RDX. It has excellent stowage qualities, but, because of its sensitivity, it is shipped immersed in water like an initiating explosive.
The velocity of detonation is 28,000 feet/second at a density of 1.70. Its Laboratory Impact Value is 34. Its Bullet Impact Value is 0. Its color is white.
PETN resembles RDX in its characteristics. It is somewhat more sensitive, but almost equal in power and brisance. It is appreciably more sensitive to percussion and impact than Tetryl and is, therefore, not used alone as a booster, though it is being used as a base charge in some compound detonators in the way Tetryl is. The tendency of PETN to burn is much less than that of similar explosives. Its main use alone in the service is in primacord. When use alone, PETN is combined with a small quantity of wax to desensitize and lubricate it, and is loaded by pressing. It is important to know that PETN in primacord is very insensitive to flame, shock, and friction, and therefore must be detonated by a cap.
The velocity of detonation of PETN is 26,000 feet/second. The velocity of detonation of primacord is 20,500 feet/second. Its Laboratory Impact Value is 22. Its Bullet Impact Value, though, not given, would be about equal to RDX (0). Its color is white.
Haleite (EDNA, Ethylenedinitramine)
Haleite is a new explosive that probably will not be used alone, but will be used in combination with other explosives. It is somewhat more powerful than TNT. Its sensitivity is about the same as Tetryl. It melts at 180 degrees Celsius, but one report states that it may detonator in the manner of an initiating explosive at that temperature or a little lower. If loaded alone, it would be pressed.
Its velocity of detonation is 25,000 feet/second at a density of 1.5. Its Laboratory Impact Value is 46. Its Bullet Impact Value is not available.
Nitroguanidine is the explosive incorporated in the Navy's new double-based propellant powder, SPCG. It is unusual in being a high explosive that is so cool in its reaction that it explodes without flash. It is comparable in strength to TNT, and its sensitivity is of the same order.
Its rate of detonation is 24,400 feet/second at a density of 150.
Amatol, a substitute for TNT, is a mixture of ammonium nitrate and TNT; the percentage of ammonium nitrate, depending on the availability of TNT, has varied from 40% to 80%. Its power and brisance decrease with the increasing percentages of nitrate, and its sensitivity decreases at the same time. However, it is still fairly good high explosive, even when the TNT is reduced to 20%. 80/20 cannot be cast, since it is not fluid enough to pour even when TNT is molted, and it therefore must be loaded by extrusion. Amatol has a disadvantage in that it is very hygroscopic and therefore is usually protected by a sealing pour of pure TNT.
The velocite of detonation of 50/50 is 19,700 feet/second at a density of 1.54. Its Laboratory Impact Value is 93. Its Bullet Impact Value is about 100. Its color is buff.
Composition B is intended to be used a s a more powerful replacement for TNT in the loading of some of the large size G.P. bombs, and in fragmentation bombs. It will 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.
Composition B1 is a mixture of 59% RDX, 40% TNT, and 1% wax. Composition B2 is a mixture of 60% RDX, 40% TNT. The TNT cuts down the sensitivity of the RDX to a safe range and lowers the melting point to 81 degrees Celsius, allowing the material to be cast-loaded.
Composition B might be detonated at low order by bullet impact, but it is almost as insensitive as TNT in this respect . It has an extremely high shaped-charge efficiency.
Its velocity of detonation is 24,500 feet/second at a density of 1.6. Its total energy of blast in air is about 116% of that of TNT. Its Laboratory Impact Value is 79. Its Bullet Impact Value is 79. Its color is yellow to brown.
Torpex is one of the explosives developed during this war to be used mainly in underwater ordnance. The original Torpex (Torpex 1) was a mixture of 45% RDX, 37% TNT, 18% Aluminum powder (1% wax added). It is used in mines, torpedo warheads, and depth bombs. Torpex is more sensitive than TNT; its bullet impact and drop test sensitivities are of the same order as those of Tetryl. It is quite stable in stowage, though it produces gas, causing pressure in the case. It is insensitive enough to stand all normal handling. Its melting point is low enough for it to be cast-loaded.
Its velocity of detonation is 24,000 feet/second at a density of 1.72. It is 141% as powerful as TNT. Its Laboratory Impact Value is 53. Its Bullet Impact Value is 48. Its color is slate gray.
DBX (Depth Bomb Explosive)
DBX is another aluminized RDX mixture, and its name suggests its intended use. It is 21% RDX, 21% Aluminum Nitrate, 40% TNT, 18% Aluminum. It was designed to replace Torpex, which is closely resembles in sensitivity, strength, brisance, and energy of shock in water, but half of the strategic RDX in Torpex is replaced by Ammonium Nitrate in DBX. It will probably not be used, as the present supply of RDX seems adequate to meet the demand. DBX can be cast, though its melting range of 98-105 degrees Celsius is about the upper limit.
Its velocity of detonation is 22,300 feet/second at a density of 1.68. It is 143% as powerful as TNT under water. Its Laboratory Impact Value is not given. Its Bullet Impact Value is 51. Its color is gray.
Next Time: High Explosives Inventory (Part 2)