The submarine drones that could depower Trident

By James O’Malley

It has been constant political background noise for years, but soon the politicians are finally going to have to make a decision: should our Trident nuclear deterrent be renewed for another generation?

The Trident system consists of four nuclear submarines – of which at least one is at sea at all times, hiding in the shadows under the water. The idea is that they enable Britain to have an independent “second-strike” capability, so that if the worst happens and London is reduced to a smouldering ash-filled crater, Britain will still be able to unleash the same apocalyptic level of destruction on Moscow, Beijing or whichever villainous power fired first.

The argument as to whether Britain needs nukes or not is contentious enough, but there is one other potential problem that Trident could face in the coming decades: a new generation of submersible drones that could soon render it useless.

Improving drones

Remotely Operated Vehicles (ROVs) have been used to explore under the sea for decades, but these have always remained tethered to the ship, and have been driven by remote control by someone sat at the surface. The challenge for scientists now is to build autonomous underwater vehicles (AUVs) that can operate truly independently.

Such drones would obviously be a threat to Trident, because they could be deployed for long periods of time – and in large numbers – without requiring human operation, making global ocean surveillance a genuine possibility.

AUVs face different challenges to aerial drones. For example, although weight is less of an issue under water, radio waves do not easily travel beneath the surface. This means that any such drones can’t easily be guided by GPS and must instead rely on onboard sensors. It also makes transmitting collected information more difficult.

In March, the National Oceanography Centre (NOC) won £2.9 million of government funding to continue work on its Autosub programme. Based in Southampton, over the past several years the project has made some impressive leaps towards solving these marine-specific challenges. The public face of the project is all about civilian-focused applications such as in scientific research, but it’s easy to imagine how the technologies could be deployed for military purposes.

For example, the Autosub3 has been tested a number of times in 24-hour missions in which it has been sent to collect data from beneath polar ice, and it has returned every time. The way it solves the GPS problem is rather clever: it uses a technique called dead reckoning, which was used by mariners long before we had satellites. The idea is that once you know one fixed position, you can use your knowledge of the speed and direction that you’re travelling to calculate your position. The Autosub3 uses sonar waves bounced off the ocean floor to figure out its speed by comparing the Doppler effect. For direction, it uses a fibre-optic gyroscope, which apparently means it makes errors of only about one metre for each kilometre travelled.


There is one problem AUVs have in common with UAVs: battery power. According to NOC, the Autosub3 is powered by the same “D” batteries that you might find in a torch (the big, thick batteries that are about twice the size of a AA battery). It’s pretty power-hungry, though: it required 5,000 of them to run.

This means that the AUV has been able to explore undersea ice caves in the Antarctic that would otherwise be inaccessible to humans. And amazingly, this isn’t the cutting edge – this was achieved back in 2009.

Mobile technology

More recently, NOC scientists have been taking advantage of the revolution in mobile technology thanks to a booming smartphone industry. The tiny, fast and power-efficient processors that we use on our phones have also made more powerful UAVs possible. The Autosub LR (as in “long range”) can – in theory – last up to six months, with a range of 6,000km. With this range, it could also be launched much more cheaply – being launched from the shore and then travelling to its destination, rather than requiring a polar research vessel to take a trip.

In 2014, the Autosub LR was launched for the first time off the coast of Ireland, and it wasn’t a 100% success. It lasted three days – surfacing each day to transmit data back – before the scientists lost signal. It was presumed lost, but eventually made contact using its emergency satellite beacon. Scientists were able to retrieve the AUV and are currently in the process of figuring out what went wrong. But what’s clear is that even though this test ended badly, this is the sort of AUV that could conceivably be tasked with hunting down nuclear submarines.

Drones that can manoeuvre themselves would also make it harder for submarines to get away once they’ve been detected. Currently the best detection system to figure out what is going on beneath the waves is the sonobuoy. These are missile-shaped devices that are usually dropped out of planes, which then deploy a parachute and land gracefully on the water. At this point, a sonar is dropped beneath the surface and scanning can begin. Signals are then sent back to the aircraft flying above, or perhaps a satellite. The problem with them currently is that they’re static, so if they pick up an enemy sub, the bad guys can simply float off somewhere else. A UAV system, by contrast, could conceivably lock on to the signal and essentially chase it.

The actual detection technology is getting better, too. Although sonar is still the primary means of detection, techniques are being developed that use other types of sensing – including optical. Processing signals is also improving. Relatively recent research shows that scientists are improving the range at which they can model the contents of the ocean – with man-made objects giving a distinct acoustic pattern to fish and other natural material.


Underwater networks

Another other area in which UAVs are driving new research and technology is in networking. As mentioned above, radio waves don’t travel well under water – which makes it hard to feed data back to base. But if this problem can be solved, it could be hugely useful to whoever manages to crack it – and could conceivably undermine Trident’s ability to hide.

This is because we shouldn’t just think about individual vehicles working independently when we think about UAVs. What is more likely is that we’ll eventually reach a point where UAVs operate in packs – patrolling the ocean together.

For example, Georgia Tech Research Institute has a programme working on UAVs that can collaborate without human intervention – so that one drone can call over another that perhaps has a different type of sensor on board.

To get around the communication problem, the Institute’s current research is using acoustic communication techniques – essentially the same sound energy as found in sonars – to send data between UAVs. The problem is that data transfer is very slow compared to radio frequencies. The Institute has expressed hopes though that it will actually carry out further research on radio signals – although the trade-off will presumably be that any radio communications require more power to boost the signal so it can travel through water.

The danger to Trident is that UAVs hunting in packs will bring the same efficiencies that a pack of wolves has over an individual wolf looking for its prey. If communication technologies improve too – as seems likely – then this will enable even greater efficiencies.

Troubled waters?

Given these advances, and the new technologies that are predicted to be close, there’s an awkward question: is renewing Trident pointless? The deterrent needs to last us an entire generation – both for actual defence reasons, and in order to justify the enormous price tag.

We can take some solace in the fact that the technologies talked about here are being developed by the West – and moreover for non-military applications – rather than any likely adversary. But this doesn’t mean Trident is safe, nor that other countries aren’t already pursuing similar, albeit militarised projects: if the Cold War arms race taught us anything, it’s that any technological advantage doesn’t remain an advantage for long. (And you only have to glance at consumer technology to see that China is just as capable of producing world-leading technologies as we are.)

“For all the advances in UAV tech, it’s important not to underestimate the sheer scale of the challenge involved in detecting a submarine.”

For all the leaps and bounds being made in UAV tech, however, it’s important not to underestimate the sheer scale of the challenge involved in detecting a submarine, nuclear or otherwise. As Andrew Tate, a former UK Royal Navy officer, writes in Jane’s Navy International, “The most difficult challenge in anti-submarine warfare is to find the patrolling SSBN (nuclear-powered ballistic missile-carrying submarine). It will operate at slow speed to minimise its signature, will not make any transmissions, will rarely return to periscope depth, and may operate in a vast area. For example, the North Atlantic Ocean covers more than 15 million square miles… Persistent UAVs, even with comparable or better sensors, would not change the odds significantly.”

The good news is that even if Trident faces challenges from advances in underwater drone technology, it could still have some use. Simply put: Trident could still be the best option available. The comparison to make isn’t between having Trident submarines and not having Trident submarines at all. The question is whether a submarine delivery system is still the best option compared to aircraft, missile silo or any other way of delivering a warhead to its destination.

Similarly, although Trident will likely become less easy to hide, if it can remain relatively well hidden, it will still remain a better option than a means that cannot be hidden at all.

So should we renew Trident? That’s a question for politicians and ethicists – but whatever we decide, we should probably think about technological evolution first.

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