against kinetic energy rounds but at the expense of adding considerable weight to the tank, as depleted uranium is 1.7 times denser than lead. The first M1A1 tanks to receive this upgrade were tanks stationed in Germany. US-based tank battalions participating in Operation Desert Storm received an emergency program to upgrade their tanks with depleted uranium armor immediately before the onset of the campaign. M1A2 tanks uniformly incorporate depleted uranium armor, and all M1A1 tanks in active service have been upgraded to this standard as well. This variant was designated as the M1A1HA (HA for Heavy Armor). The M1A1 AIM, M1A2 SEP and all subsequent Abrams models feature depleted uranium in both the hull and turret armor. Each Abrams variant after the M1A1 have been equipped with depleted uranium armor of different generations. The M1A1HA uses first generation armor, while the M1A2 and M1A1HC use second generation depleted uranium. The M1A2 SEP variants have been equipped with third generation depleted uranium armor combined with a graphite coating. The M1A2C also features increased physical line-of-sight turret armor. For the M1A1HA, Zaloga gives a frontal armor estimate of 600 mm vs APFSDS and 1300 mm vs HEAT in M1 Abrams Main Battle Tank 1982–1992, nearly double the original protection of the Abrams. In M1 Abrams vs T-72 Ural, he uses different estimates of 600 mm vs APFSDS and 700 mm vs HEAT for the front hull and 800 mm vs APFSDS and 1300 mm vs HEAT for the front of the turret. The protection of M1A2 SEP is a frontal turret armor estimate of 940–960 mm vs APFSDS and 1,320–1,620 vs HEAT, glacis estimate of 560–590 mm vs APFSDS and 510–1,050 vs HEAT, and lower front hull estimate of 580–650 mm vs APFSDS and 800–970 vs HEAT. The M1A2 SEPV3 increased the LOS thickness of the turret and hull front armor; total armor protection from this increase is not known. In 1998, a program was begun to incorporate improved turret side armor into the M1A2. This was intended to offer better protection against rocket-propelled grenades more modern than the baseline RPG-7. These kits were installed on about 325 older M1A2 tanks in 2001-2009 and it was also included in upgraded tanks. The Abrams may also be fitted with explosive reactive armor over the track skirts if needed (such as the Tank Urban Survival Kit) and slat armor over the rear of the