Twenty-five ships of the class (DE-1052, 1056, 1063–1071 and 1078–1097) were refitted with the AN/SQS-35(V) Independent Variable Depth Sonar, an active sonar operating at about 13 kHz. The IVDS' sonar transducers were packaged within a 2-ton fiberglass-enclosed "fish" containing the sonar array and a gyro-compass/sensor package launched by the massive 13V Hoist from a stern compartment, located just beneath the main deck, to depths of up to . The IVDS could take advantage of water layer temperature conditions in close-range (less than ) submarine detection, tracking and fire-control. The AN/SQS-35 "fish" was later modified to tow an AN/SQR-18A TACTASS passive towed array sonar. The DASH drone proved unreliable, and following its withdrawal in 1973, the ships' helicopter facilities were expanded to accommodate the larger, manned, Kaman Seasprite LAMPS 1 helicopter.