3rd Radio Research Unit (RRU)
The United States Army Security Agency (ASA) was the United States Army's signals intelligence branch from 1945 to 1976. The Latin motto of the Army Security Agency was Semper Vigilis (Vigilant Always), which echoes the declaration, often mistakenly attributed to Thomas Jefferson, that "The price of liberty is eternal vigilance."

Although most ASA units focused upon SIGINT (signals intelligence) most if not all ASA units contained HUMINT (human intelligence) specialists as well, mostly interrogators and counter-intelligence specialists. At the end of the Cold War era, some ASA units also were staffed with ELINT (electronic intelligence) specialists and warrant officers, which incorporated field ECM (electronic counter-measures and field ECCM (electronic counter-countermeasures) such as tactical jammers, direction finders, electronic signal decoys, and captured/repurposed Warsaw Pact radio and communications equipment.