Radar Sensors

Radar sensors have been used since World War II for the detection of surfaced or snorkeling submarines. Back then, submarines relied upon their batteries for submerged operations. Eventually their batteries would become drained to the point where they were forced to return to the surface and operate their diesel engines to re-charge the battery. While surfaced, the submarine was extremely vulnerable to detection by both radar and visual sensors. The addition of a snorkel enabled the submarine to operate its battery-charging diesel engines while minimizing its exposure to radar and visual sensors. Additionally, the background clutter of the surrounding ocean waves limited radar and visual detection. Also, the development of submarine-based electro-magnetic sensors provided the submarine commander with suffficient warning to dive if approaching radar emissions were detected.

Eventually, nuclear submarines where developed which eliminated the need to periodically recharge the batteries. Despite this significant advance, not all nations were able to build nuclear submarines due to financial and technological reasons. Those nations which remain committed to diesel power have pursued technology which limits the number of times the submarine has to recharge its batteries. However, many submarine commanders must still use their periscopes to provide final visual classification of targets prior to attack. Because of this requirement for target verification, radar systems are still used to detect submarine periscopes.

Today's airborne radar systems must be lightweight yet sufficiently capable for ASW operations, long-range detection and surveillance of surface vessels, airborne navigation, and weather avoidance. For that purpose, many Air ASW radar systems use different radar frequencies, scanning speeds, transmission characteristics, pulse lengths, and signal processing methods that reduce background sea clutter and enhance radar returns from exposed pericopes and submarine hulls. The hostile submarine using electro-magnetic sensors, however, can still detect ASW aircraft radar emissions at a much greater distance than the aircraft can detect the submarine by radar. Nevertheless, the threat of radar detection is sufficient to keep the submarine submerged. Radar systems now used aboard U.S. Navy ASW aircraft include the AN/APS-115 (P-3C), AN/APS-124 (SH-60B), and AN/APS-137 (S-3B, some P-3Cs).