M1 "Abrams" main battle tank modernization M1A1 as new modification had a number greater abilities than it's predecessor. M1A1 differed firstly in greater firepower and increased defense. Since 1988 M1A1 modification was produced with built-in precipitant uranium armor. In 1986 first modernized M1A1 "Abrams" entered service in US Armed Forces. Firstly they were deployed in US tank forces in German Federation Republic.