An ASW concept for the future (2020's)

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This is about the 2020's.

Imagine a swimming pool that's filled with water, and on the water's surface are footballs. In fact, there are more footballs than needed to cover the entire area - several spare ones are sitting atop others. Now remove a ball from this picture - the others would be move by gravity and the gap would be filled.

Now replace this mental picture with the ocean - the balls are small ships, most of them at very, very low speed if not drifting. Some of those ships have a low frequency active sonar* emitter that make a lot of low frequency noise (the noise that apparently drives whales and thus Greenpeace mad). Their crews are on other ships a mile or two away, controlling this loud emitter ship from safe distance. That's advisable because being a loud emitter, every hostile submarine has the worst wishes for it. The controlling manned ship nearby on the other hand is irrelevant; remote control could just as well be by a satellite communication backup.

A different kind of ship emits no relevant noises at all, it's merely drifting. It's using an entirely passive sonar array that's meant to pick up the echoes of the noises made by the low frequency sonar emitters.

This is a multistatic sonar network with acceptable odds of crew survival. It can cover a huge area at affordable expenses. Any submarine could be detected except in areas where very tricky sea bottom shapes and tricky sonar phenomena make detection difficult. It wouldn't detect 100% of submarines quickly, but the probability of detection would be very high.  Hostile air power could sweep the sea clean of this, but my assumption for now is that this is not an area in range of hostile air power.

What to do with a suspected contact? It might be one of many false positives. This is the time for another kind of drone; they're floating and drifting on the surface as well, waiting for an order by radio. The two of them closest to a suspected contact get tasked to investigate. They intercept, use an imaging active sonar and return to surface to transmit the result by radio. The imaging sonar could show a hostile submarine type, or both investigation drones fail to report back in time - both would lead to the contact being considered an actual hostile submarine, since a friendly submarine would be discernible visually and it would decipher an identification code embedded in the imaging sonar's emissions and thus not destroy the investigator drones.

Finally, the area commander would want to engage a detected and confirmed hostile submarine. During the 1990's he would have dispatched maritime patrol aircraft or helicopters - particularly the latter ones might also have been employed for confirming the contact with a dipping sonar. But this is the 2020's, and hostile submarines are known to have submarine-to-air missiles. To protect helicopters and aircraft against those was much too expensive. Instead, the area commander would have a revival of an old concept at hand - ASW-SOW or "Sea Lance", a vertical launch rocket with impressive range and a lightweight anti-submarine torpedo as warhead. Development of such munitions was held back in favour of gold-plated helicopters back when submarine-to-air missiles weren't known to be common. These can be launched through satellite or other radio communication; their storage is in simple containers on some, but not all of the ships, mostly hidden from (periscope) sight.

A pattern of three such missiles is launched, impacting in a triangle formation around the contact and engaging it with a "no escape" intent. The optimization of the lightweight torpedo warheads and their formation attack pattern are the reason why no investigator drones have a secondary "kill" purpose; they would be ineffective by comparison and throw away a valuable imaging sonar.

The submarine's only chance of survival is now the employment of countermeasures, but the investigator drones are back in action (if they survived) and attempt to document any countermeasures employed in order to refine future attack methods.

The most fascinating thing: Not a single warship is needed to secure a shipping lane 100 nm wide and hundreds of nm long. The only hardware employed were small civilian ships turned into auxiliary warships and munitions / drones.

A convoy system isn't required either, since the security effort is proportional to the area (required length and required width), threat (engagement range submarine -> cargo ship) and ambition (density and desired width) - it's independent of the quantity of secured ships on that shipping lane (related link).

We're not going to see this in the 2020's by any of the major navies known today unless they lose much of their conventional forces as did the USN in 1941 Pearl Harbour, provoking its modernization into a carrier-centric force. The reason is the same; back in the 1930's the battleship and cruiser lobby wanted as many battleships and cruisers as possible, with many, many career opportunities for officers.

No established major navy would want to build itself into something that requires almost no fancy warship hulls with almost no jobs and career opportunities for officers, and certainly they cannot stand the idea of a navy ASW branch largely consisting of thousands of containers in dry storage, waiting to be used to create an auxiliary warship and drones ASW force in wartime.

P.S.: Everything described herein has been technically feasible since the mid-1990's at the latest.

*: "The array creates a dish shaped pattern of very loud, low frequency, variable broadband sound (235 dB (...) @ 100-1000 Hz) that reaches out roughly 100 miles. The towed array is deployed about 100 meters deep at three knots, pulsing on a 10% duty cycle. In recent experiments, Low-Frequency Active (LFA) system has detected submarines at long ranges." source

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