The AN/AQS-13 series was a helicopter dipping sonar system for the United States Navy. These systems were deployed as the primary inner zone anti-submarine warfare (ASW) sensor on aircraft carrier based helicopters for over five decades. Companion versions with the AQS-18 designation were exported to various nations around the globe.
Purpose
Airborne sonar systems provide a light-weight, mobile detection sensor for locating and tracking submarines. Although limited in performance compared to larger, ship-mounted sonars, these helicopter-borne systems have the advantage of rapid deployment/retrieval times, and rapid transition between search areas. Additional advantages over ship sonars include absence of flow noise and engine noise, and the elimination of Doppler shift induced by a moving signal source. Deployed from Aircraft Carriers or other ships, these systems enable the aircraft to locate, identify and attack submerged targets within the flight radius from the home ship.
Description
The AQS-13 systems are all primarily active sonar transmitting in the upper end of the medium frequency sonar range. These systems offered the additional capabilities of voice communication, bathythermography and rudimentary passive sonar. Helicopter borne active sonar has significant advantages over other sensors and is especially effective in the inner zone where noise from the ships of the carrier battle group can interfere with passive sensors. The components of the AQS-13 are informally divided into two groups, the "wet end" and "dry end." The "dry end" involves the processing of the acoustic signals to obtain tactical data. The "wet end" components are those necessary to deploy the acoustic unit into the ocean and retrieve it. These "wet" components include the acoustic elements in a submersible unit, the reel & cable and reeling machine. The hydrophone and projector elements are housed within the submersible unit or transducer. The transducer, also called the "dome", a term borrowed from ship-board sonars, is lowered or "dipped" from the helicopter on a cable by means of the hydraulic reeling machine. The dip depth of the transducer is selected by the operator to achieve the maximum detection probability at the dip location on that particular day as determined by the study of ocean conditions (see Underwater Acoustics). During active search, the acoustic pulse is emitted from the projector assembly. Echos or "returns" are received by the hydrophone, routed through the sonar cable, processed in the aircraft and displayed on a cathode ray tube (CRT) in a plan position indicator (PPI) format. Returns were also processed and made available to the RO-358 chart recorder in the AQS-13E and earlier systems. This data was made available to the aircraft tactical computer in the AQS-13F. The various functions were selectable by the operator, such as pulse lengths, range scales and other modes to enhance operations for the particular conditions. Sensor elements on the reeling machine monitor the relative angle of the deployed sonar cable and provide flight reference signals to the aircraft stabilization equipment in order to maintain a steady hover position over the submerged transducer. Tactical data of the target is obtained from the acoustic returns, including range, bearing and relative speed. Later versions of the AQS-13 were also capable of processing acoustic signals transmitted to the aircraft from sonobuoys.
History
AQS-13
The AQS-13 system was introduced to the US fleet aboard the Sikorsky SH-3D anti-submarine warfare helicopter in the mid-1960s. (See military helicopter/maritime helicopters) This was an upgrade from the AQS-10 system carried aboard the SH-3A helicopter. The AQS-13 offered an improved reeling machine and longer cable or "wet-end" than the AQS-10. The "dry-end" components of the system remained essentially the same as the AQS-10. Developed in the 1950s, these components utilized primarily vacuum tube technology. The RO-358 chart recorder provided a means of recording a permanent record of target data as well as additional means for target evaluation.
AQS-13A
The AQS-13A system was an upgrade to the basic AQS-13 system incorporated into fleet systems in the late-1960s/early-1970s. The upgrade was primarily to incorporate built-in test equipment (BITE) circuitry, providing a method for testing system circuitry in the sonar set.