The AN/UQQ-2 Surveillance Towed Array Sensor System (SURTASS), colloquially referred to as the ship's "Tail", is a towed array sonar system of the United States Navy. SURTASS Twin-Line consists of either the long passive SURTASS array or the Twin-line array consisting of two shorter passive arrays towed side by side. The Twin-line Engineering Development Model was installed on USNS Assertive, and the first production model was installed on USNS Bold. Both ships are no longer serving as SURTASS units.