Recent comment about the development of drones that can detect and track submarines, with the inference that they will easily find and follow Trident submarines reminds me of an occurrence 35 years ago, when a CND activist approached my brother and asked if he would sign a petition, protesting against the proposed basing of cruise missiles at Greenham Common. Feigning ignorance my brother asked what a cruise missile was. The activist explained that it was a small nuclear armed missile that on launching, deployed short wings and flew to the target. "Rather like a pilotless aeroplane" my brother remarked. "Exactly" replied the activist. "Sorry mate" said my brother, "you're too late, we've had them here for years; the only difference is that the present cruise missiles have pilots in them". My brother did not sign the petition.
So submarine hunting drones? Yes we've had those for years, albeit with people in them. They are called destroyers, frigates, submarines (both nuclear SSN's and conventional SSK's), aircraft (rotary and fixed wing) and satellites. Of course, unmanned drones may be cheaper to produce and operate than the manned versions and so could be distributed in far greater numbers, with possibly greater persistence (although that is questionable). I suggest however that unmanned decoy drones, that would emulate the signature of a Trident submarine would be even cheaper to produce and could lead the sub hunting drone a merry chase. Submarine hunting technologies have been in development for over 100 years and that research will continue. Likewise the technologies aimed at keeping the submarine hidden have been in development for a greater period than that and they also will advance. Shakers that neutralise a submarine's sound signature are being developed, the modern version of degaussing and non magnetic steels can be used to mask the magnetic signature, plate coolers help to dissipate heat, anechoic tiles absorb sonar pulses, decoys (both manned and unmanned) draw opponents away but if all else fails a Trident submarine is not without the means to deflect the weapons aimed at her or the teeth to defend herself and kill her hunters. Another consideration is that the unmanned drone, by the very fact that she is hunting instead of hiding, will be far more visible than her prey; thus she will be relatively easily avoided and vulnerable to interference and/or neutralisation.
Seabed arrays of listening and upward looking detectors have also been mentioned as another development that will detect Trident submarines but, like the drones, these also are not new. The SOSUS/ACOUSTINT/FDS listening systems have been in development and/or use since the 1950's, with mixed success. As the submarines have become quieter their effectiveness has been reduced and they are not beyond interference by the trawling up of their cable network or the sensors themselves. During the Cold War, submarines and surface vessels, of both sides, planted listening devices in the back yards of their opponents. An ex US navy diver told me that they had once found a Soviet listening device on the seabed at the entrance to Holy Loch on the west coast of Scotland, where the US Polaris submarines were based.
System and counter system have always been in development and they will continue to be so. It should be borne in mind however that equipment that performs well in controlled tests, frequently fails to produce the desired results when practical operating difficulties become apparent in the field! In the forthcoming debate on whether to renew or not to renew the Trident nuclear deterrent this should be borne in mind, so that suggestions of systems that will sweep away the cloak of invisibility the deep oceans afford to quiet submarines are scrutinised with a critical eye. In this way proportionality can be maintained and it may be seen that a quiet submarine that does not want to be found is still a very small needle in an extremely large haystack.