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Depleted Uranium [DU] History

The Army uses alloyed DU in the 25, 105, and 120 millimeter (mm) kinetic energy cartridges. The Bradley Fighting Vehicle uses the 25 mm cartridge (not released for use as of May 1995) in its chain gun. The M1 and M60 series tanks use the 105 mm cartridge; the Army also plans to use the 105 mm in the main gun of the XM8 Armored Gun System. The M1A1 and M1A2 Abrams Tank main guns use the 120 mm cartridge. DU is used as an armor component on the M1 series heavy armor (HA) tanks. Small amounts of DU are used as an epoxy catalyst for the M86 Pursuit Deterrent Munition (PDM) and the Area Denial Artillery Munition (ADAM).

During the late 1950s, the primary material used for kinetic energy, armor-piercing projectiles was tungsten carbide. When first fielded, tungsten carbide represented a quantum improvement over its nearest competitor, high carbon steel. Its higher density (approximately 13 gm/cc) gave it superior penetration performance against existing armor targets. With the advent of double and triple plated armor in the 1960s, however, tungsten munitions showed a tendency to break up before penetrating the layered armor. This deficiency spurred the development of new alloys and materials capable of defeating any armored threats.

In response to the new operational requirements, a succession of metal alloys were evaluated. Initially, the UK Government developed a higher density tungsten alloy consisting of 93 percent tungsten and 7 percent binder tungsten alloy (WA). The new WA alloy had a density of 17 gm/cc versus 13 gm/cc for tungsten carbide. From 1965 to 1972, the US Army conducted a parallel development program for the 152mm XM578 cartridge which was co-developed with the MBT-70 Tank. The XM578 cartridge used a tungsten alloy that was slightly denser than the British alloy consisting of 97.5 percent tungsten and 2.5 percent binder, which had a density of 18.5 gm/cc.

Throughout the 1960s and early 1970s, the Army developed a successive series of improved 105 mm rounds (the primary main gun caliber on M-60 and developmental XM-1 series tanks) using the denser 97.5% tungsten alloy. The first of these rounds were the XM735 and XM774 cartridges derived from the XM578 cartridge program. These alloys proved sufficient to meet the Army's operational requirements. At the same time, the Army continued to investigate applications for depleted uranium [DU].

In the mid-1970s, it had become evident that the latest generation armor was impervious to tungsten carbide penetrators. Picatinny engineers had been working on improving the properties of DU, an especially dense metal, and saw potential for its use in the 105mm M774 cartridge. In conjunction with the Department of Energy's Battelle Pacific Northwest Laboratories, Picatinny developed the unique material purity and heat treatment process necessary to produce a hard, touch U3/4Ti, Uranium/Titanium alloy penetrator.

The next evolution of 105mm KE cartridge was the M833. This projectile incorporated a longer monolithic DU penetrator, which made it go faster and reduced the weight of the sabot by making longitudinal cuts. This gave the projectile the strength it needed on launch and the penetration necessary to defeat the threat. As effective as this cartridge was, threats became even more sophisticated and it was replaced with the M900 Depleted Uranium projectile. Currently in its fourth generation, this cartridge is the Army's primary antiarmor 105mm tank ammunition, and is also used by the Marine Corps. The M900 can penetrate the frontal slope of enemy armor systems and has excellent accuracy at all combat ranges because of the penetrator and sabot design.

One of the Army's first uses of DU was as a ballistic weight in the spotting round for the Davy Crockett missile warhead. Additionally, in the early 1960s, the Army tested a four-alloy "UQuad" containing DU in experimental tests on the 105mm and 120mm Delta Armor Piercing Fin Stabilized, Discarding Sabots (APFSDS). Tungsten continued to be favored over DU, however, for two main reasons: 1) DU was still developmental, and inconsistencies with the alloys in the manufacturing process were a persistent problem; and 2) penetration tests against older Soviet tanks and similar targets failed to show the clear penetration superiority of the DU round.

In the mid-1970s, as it became clear that the latest-generation armors might prove impervious to tungsten carbide penetrators, the Army's focus on improved tungsten alloys began to shift. At the same time, parallel Air Force and Navy tests using smaller-caliber (20-, 25-, and 30mm) ammunition had demonstrated quite convincingly the clear penetration superiority of DU rounds.

In 1973, the Army evaluated alternatives for improving the lethality of its 105mm M68 tank gun. This effort grew into the XM774 Cartridge Program which, after an extensive developmental testing and evaluation program, selected depleted uranium alloyed with ¾ percent by weight titanium (U-3/4Ti). The selection of U-3/4Ti derived in part from improved designs and alloys that allowed the DU core to withstand high acceleration without breaking up. In the 1960s, tungsten alloys used in the XM578 projectile had to be encased in a steel jacket to withstand the extreme firing velocities of the 152mm gun, reducing the penetrating effectiveness of the tungsten cartridge. The new U-3/4Ti alloy overcame these early limitations for large caliber munitions.

Development of U-3/4Ti ushered in a new generation of penetrators for the Army. Since the selection of DU for the XM774 cartridge, all major developments in tank ammunition have selected DU, including the 105mm M833 series and the 120mm M829 series (the latter being the primary anti-armor round used in the Gulf War). This pattern continues today, with the latest generation of the 105mm M900 series and the 25mm M919 for the Bradley Fighting Vehicle.

In the early 1970s, the Air Force developed the GAU-8/A air to surface gun system for the A-10 close air support aircraft. This unique aircraft, designed to counter the massive Soviet/Warsaw Pact armored formations spearheading an attack into NATO's Central Region, was literally designed and built around the GAU-8. This large, heavy, eight-barreled 30-mm cannon was designed to blast through the top armor of even the heaviest enemy tanks. To further exploit the new cannon's tremendous striking power, the Air Force opted to use the depleted uranium U-3/4Ti, a 30mm API round. A comprehensive Environmental Assessment of the GAU-8 ammunition was released on January 18, 1976. The report stated that the proposed action was expected to have no significant environmental impact and that the "biomedical and toxicological hazards of the use of depleted uranium (DU) in this program are practically negligible." The A-10 aircraft was deployed to United States Air Forces in Europe (USAFE) in 1978.

The Navy's Phalanx Close-In Weapon System, or CIWS was designed for terminal (last-ditch) defense against sea-skimming missiles. The Navy evaluated a wide range of materials before deciding on DU alloyed with 2 percent molybdenum (DU-2Mo). Phalanx production started in 1978, with orders for 23 USN and 14 Foreign Military Sales systems; however, subsequent budget cuts reduced these numbers. In 1988 the Navy opted to transition the CIWS 20mm round from DU to tungsten. The Navy made the decision based on live fire tests that showed that tungsten met the Navy's performance requirements while offering reduced probabilities of radiation exposure and environmental impact. It should be noted that the "soft" targets the CIWS was designed to defeat-anti-ship missiles at close range-are far easier to destroy than "hard" targets like tanks. Substantial stocks of DU ammunition delivered prior to that date remain in the inventory.

DU munitions were first used in the Gulf War of 1991. A total of 320 tons (290,300 kilograms) of DU projectiles were fired by the US during the Gulf War. DU friendly fire and accidental fire incidents contaminated a total of 31 US combat vehicles (16 Abrams tanks and 15 Bradley armored vehicles) in the Gulf during 1990-1991. These incidents, and the resultant cleanup and recovery operations, exposed a number of soldiers to depleted uranium. Those with the highest exposures were in, on, or near vehicles when they were struck.

US Air Force A-10 Thunderbolt II aircraft fired approximately 10,000 30mm DU rounds (3.3 tons of DU) at 12 sites in Bosnia-Herzegovina in 1994-1995. In 1999, they fired nearly 31,000 DU rounds (10.2 tons of DU) at 85 sites in Kosovo.