Low-frequency sonar can detect beyond direct path as sound bends downward and returns at convergence-zone ranges. A convergence zone may be about five nautical miles wide, leaving too much positional uncertainty for simply firing a torpedo-carrying missile into it. Norman Friedman therefore places the generally useful ship-launched missile range near 20,000 yards, with exceptions where sound trapped in layers extends useful detection. The planned extended-range ASROC for SQS-26 was cancelled during the Vietnam War. Later VL-ASROC matched the SQS-53's roughly 20,000-yard direct-path range. Japan developed a Type 07 equivalent carrying an indigenous lightweight torpedo, while South Korea's Red Shark is described as carrying its White Shark torpedo.
Chapter · 25:02-26:20
Sonar geometry caps useful ASW missile range
Long sonar detection does not automatically yield a precise firing solution, so modern ship-launched ASW missiles are matched to useful direct-path ranges.