The United States Army Regimental System (USARS) is an organizational and classification system used by the United States Army. It was established in 1981 to replace the Combat Arms Regimental System (CARS) to provide each soldier with continuous identification with a single regiment, and to increase a soldier's probability of serving recurring assignments with their regiment. The USARS was intended to enhance combat effectiveness by providing the opportunity for a regimental affiliation, thus obtaining some of the benefits of the traditional regimental system.

The 3rd Air Defense Artillery Regiment is an air defense artillery regiment of the United States Army, first formed in 1821 as the 3rd Regiment of Artillery.