Anti Submarine Warfare Are the Oceans Getting Darker?

ASW is the toughest element of warfare at sea, and the dice are overwhelmingly loaded in favour of submarines. What is worse, is that submarines are getting quieter, deadlier and more numerous by the day. Naturally, the world is wondering what to do about this fast-rising menace. What can contain them? What do we throw at them? It is an asymmetric contest. Or is it really so? Here is a perspective.

Issue: 5 / 2020 By Commodore G. Prakash (Retd)Photo(s): By General Dynamics Canada
Having realised the difficulty in detecting, tracking and destroying submarines, not letting the submarine succeed, was adequate ASW

What History Promises

The more clearly we see the past, the more clearly can we see the future. In the case of ASW, at the beginning, a bewildering variety of material and tactical countermeasures had to be thought up to contain submarines, with massive investments and even nationwide appeals for ideas in Britain. All these, sadly didn’t guarantee any success. This was a harbinger of things to come. In the decades that followed, every enhancement in the submarine world caused asymmetrically expensive countermeasures. Again, with no guarantee for success. Recurring instances of alien submarines popping up undetected right next to even US aircraft carriers, ringed by some of the best sensors in the world, is a testimony to this reality. The future is not likely to be different.

A March of 100 years

The idea of the submarine as a weapon was the continuation of the age-old tactic of sinking ships by making holes in their hulls below the waterline. Though the earliest attempts to make an underwater craft dates back to 1578, the birth of a submarine that could dive, cruise under water and surface on its own, was only in 1866. Somehow, submarines were not taken seriously, till Germany was forced to change tack and adopt unrestricted submarine warfare in the aftermath of the battle of Jutland of May 31 to June 1, 1916. We have only come a few years past the 100th anniversary of this development.

Just as submarines were beginning to be taken seriously, naturally, rudimentary ASW too was also taking birth. By 1914, this was in the form of the first Depth Charges, simple contraptions that, when dropped, carried explosives into water. In some of these, even the depth at which they were to explode could be set. There were also Antisubmarine nets, bombs dropped from aircraft and armoured belts to protect ships against torpedoes.

Timeless Essentials

The advantages enjoyed by submarines and the challenges faced by those fighting them, are near permanent. Some laws of physics cause this. Ear shattering sound transmitted from sonar starts diluting and weakening as it spreads as countless rays through water. These spreading rays of sound hit many objects and come back to the sonar, which after every transmission, eagerly switches to listening out for echoes, for some time. Sadly, the echoes that come back are barely a whisper, and are hidden in a surfeit of gurgling sounds. To top it all, sound rays do not even travel straight in water. They bend based on the temperature, pressure and salinity of the water they are passing through. Sonar has to strain to figure out the presence or absence of a submarine in this audio riddle.

ASW being an expensive area, new answers are sought with technology from the world of autonomous systems, artificial intelligence, fixed seabed sensors and big data analysis

With the world having concluded that sound is the best energy for underwater detection, we are stuck with the realities of Physics. Of the three basic players in the story, viz, the sonar, the sea, and the submarine, only the first is under the control of the side attempting ASW. The rest is, either with God or the enemy. And it is difficult to tell which of them is worse for ASW. Sadly, the very limits may have been reached in sonar design. Hence the array of ‘future’ solutions, which now entices the ASW world.

A History of being Reactive & Speculative

Britain came up with convoys and armed merchant ships, called Q Ships as counters. Their ships even learnt to ram submarines as the submarines of those days would often land up as sitting ducks themselves as they could do most of their offensive work only from the surface. Rudimentary progress was also being made in other areas. Mines, to deny parts of the oceans to submarines, visual surveillance from the air and blockading enemy’s submarine bases being some. But submariners braved all this, as well as poisonous gases from batteries and horrible living conditions, with sheer grit and human spirit. They fought on, virtually with death just a breath away. The result, for ASW, was as much proliferation of ideas as possible, but without any assurance that any of them would gain them decisive dominance over submarines.

As WW II raged, German submarines began to bring back memories of WW I to the Allies and the next wave of reactive ASW started. Airborne Radars, Sonobuoys, searchlights, Torpedoes, Depth Charges and Magnetic Anomaly Detectors were now born, to complement (not replace) all the ASW measures used during WW I. Aircraft, the submarine’s worst enemy, was now coming of age. But since aircraft were limited by their endurance, submarines learnt to avoid trouble by using Gambit tactics. Submarines also fought back by quieting themselves for sonars with anechoic coating on their hull which absorbed sound that hit them. They also became difficult to catch with Radar, as they swathed the upper parts of their hull with non-reflective tiles that absorbed or scattered Radar energy.

The next paradigm shift came with the Cold War. With Russia, a land power, adopting a fighting doctrine centred on long range nuclear submarine warfare and longrange bombing, US and their European allies had to find a way to keep a track of Russian submarines in the North Atlantic and North Pacific. They enjoyed two advantages. The first was that the Russians were sending out nuclear submarines. Nuclear submarines, unlike their battery run cousins couldn’t become quiet, owing to the associated machinery that had to run because of their nuclear reactors which couldn’t be shut at sea. This assured the ASW forces some level of noise, which they could use to find and track these submarines. The second advantage was that Russian submarines had to exit narrow geographically constricted spaces to enter their Operation Areas, like the Greenland – Iceland – UK gap. Here, set piece arrangements could be made using fixed sound sensing hydrophone arrays on the ocean floor, sonobuoy fields, maritime patrol aircraft to monitor the buoys, ships, helicopters, and towed array carrying ships. In addition, nuclear powered attack submarines would be available at hand to trail Russian submarines once they had come past the set piece detection arrangements. This was an extremely expensive way to wage ASW. But there was no option. ASW was virtually bleeding resources.

Geography and ASW

The story of offensive ASW, which originated in the North Atlantic, continued to be mostly centred in the same area, and to a smaller extent, in the Mediterranean. Almost all R&D happened there. USSR too developed ASW, but mostly the defensive variety. The rest of the world shopped for ASW equipment from these two sources, mostly based on their political allegiances. Everything was not available to everyone. Luckily, everything was of not much use too to most. Designed for performance in the waters of relevance to Russia, Europe and USA, that too almost entirely with noise producing nuclear submarines as the targets, tropical navies had limited use for these. But most simply shopped if they had the money. Some even received them as gifts. A few responsible countries understood the situation and put money and mind into finding answers that best suited them.

Sudden Death & Resurrection

The massive ASW set up of the west suddenly became superfluous when USSR broke up in 1991. By the time the next enemy turned up for the western nations in ten years, two important things had changed. The new enemy, was diesel powered super quiet submarines, and the Operation Areas had shifted to the warm waters of the Indian Ocean. The west made some effort to learn from the experiences of the Indian Ocean countries which had made progress. But no one would tell. ASW being an expensive area, the west had to now rethink their entire approach, anew, at great cost. New answers were sought with technology. Low frequency sensors developed for the erstwhile circumstances were tried in the new waters, with mixed results, as the God of physics wouldn’t relent. Mono-static sensors became bi-static and then multi-static. But the results remained mostly the same. Sensor based ASW of yore, was going to be useless, regardless of the money spent.

Realising the need for a whole new look, the USN developed Full Spectrum ASW, a ten-step approach to fight submarines. This new approach elevated ASW to a different level, combining diplomatic and intelligence effort at the national level, to the old elements of weapon/ sensor/ platform development. Now, the sensor-based methods of the past came way down in the list of ten. No holds were barred. Now, even submarine crew of potential adversaries were not safe in their homes. There was another great shift. Having realised the difficulty in detecting, tracking and destroying submarines, it was decided, that submarines now didn’t have to be destroyed. They just had to be ‘defeated’. In the new thought process, not letting the submarine succeed, was adequate ASW.

New Paradigms

But the sands shifted again. Before they could consolidate their new found methodologies, nuclear submarines again returned as enemy, now even more sophisticated than before. As if this was not enough, super quiet diesel submarines too joined the fray, with AIP systems further reducing their vulnerabilities. Operation Areas too expanded. Now it was the entire Indian Ocean, the China Sea and the West Pacific. The number of potential adversaries owning submarines too was increasing. With nuclear submarines of various hues becoming capable of claiming the mantle of the next real capital ships of the oceans, this is set to further increase.

The world now stares starry eyed, at a vast array of miracles promised from the world of autonomous systems, artificial intelligence, fixed seabed sensors and big data analysis. But the lessons of the past throw up concerns. And a whole lot of questions arise. For instance, what is the assurance that the confidence derived from the solutions given by artificial intelligence is any less artificial?

Navies wield their weapons and sensors to wage war on behalf of their nations. This is a legal process, where every decision to kill is taken rationally, after weighing the necessity to kill, figuring out the minimum force required, examining possible collateral damage, using gradated force and finally, killing when there is no other option. How much of this can happen, when machine is pitted against man?

Cost is another factor. While small autonomous systems can be much cheaper than the old-world manned platforms, they aren’t going to be inexpensive. Further, proliferation of submarine operating countries has expanded the areas where submarines could be encountered. What would be the quantity of equipment required to cover the humongous areas in which submarines could operate? Who can afford the great cost?

All is Not Lost

The God of physics has his fair share of curses too for submariners. The most important one is the insecurity that comes from the fact that they can make out the strength of the forces arrayed against them, only by listening out. Any effort to break surface for a ‘look’, can be suicidal. Any serious targeting with long range weapons would require external cueing, which is not easy during conflict. Hearing sonar transmissions from active longrange towed arrays or dunking sonars is a cause for worry, as the submarine will never know whether it has been detected or not. They will also never know whether modern sonobuoys are lying silently around in water, sending information up to loitering aircraft. The first sign of danger in this case could be a series of sudden explosions or the sound of torpedoes closing in. If the approach is to ‘defeat’ the submarine by harassing it, the enemy could even use explosives liberally (unmindful of the great harm this can cause to marine ecosystems) in submarine probable areas. The fact that the damage caused by explosives, increases with depth, too will play on the submariners, as they think of safety deeper down.

Is the old form of ASW, where the submarine Captain matched wits with a bunch of people who fought him from all three dimensions using their combined brains, set to change? Is the future submarine Captain going to run into a vast array of little autonomous underwater craft, whose presence he will never know? How is he to fight them? The spectre brings to the fore a most basic emotion, fear. In fear, lies the key.