There were some modernization stages incorporated during M1 Abrams main battle tank serial production. The first stage began in 1984, after the beginning of the serial production and projected to increase frontal defense and apply new M733 projectile with increased armor-piercing ability. In 1985 and 1988, the second and third modification stages were made accordingly and developed M1A1 Abrams main battle tank modernization M1A1 as new modification. It has far greater abilities than its predecessor. The M1A1 differed in greater firepower and increased defense. Since 1988, M1A1 modification has a built-in precipitant uranium armor. In 1986, the first modernized M1A1 Abrams entered service in US Armed Forces and was first deployed in US tank forces in German Federation Republic. The M1A1 main battle tanks were built in Ohio state, Lima city, national tank plant and in Michigan state, Voren city, Detroit Arsenal tank plant. General Dynamics corporation was also producing M1A1 tanks under license.