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CONCEALMENT is the key to a submarine’s success and survival. The Royal
Navy recognised this long ago when, in 1901, it established its submarine
service and took as the service’s motto Venio non videor, I come unseen.
Half a century later, when the US Navy sent its first nuclear-powered submarine
to sea in 1955, the motto became reality. The revolutionary propulsion system
on board USS Nautilus allowed submariners to spend as long as they wished
in deep water, and in doing so they effectively disappeared off the face
of the Earth.

Submarines used to be little more than submersible torpedo boats. They
could not dive for more than a day or so, and they had to spend much of
the time on the surface where they could be seen and attacked. Then, in
1944, German U-boats, hard pressed by antisubmarine aircraft, started to
employ the snorkel. This was a tube, projecting just above the water, which
was hard to detect on radar in those days. It enabled a boat to stay submerged
while running its diesel engines on its way to a patrol area or when recharging
its electrical storage batteries.

The snorkel was a big step forward; but only a decade later, the nuclear
reactor became a practical means of propulsion. With it, free from the atmosphere,
came the first true submarines. They were very fast, faster than most surface
ships battling against the waves, and their range was virtually infinite.

For quite a while, nuclear submarines were noisy, which made them vulnerable.
The next step was to make them quieter and so less detectable. Noise reduction
was important for another reason: a submarine’s own sonar sensors were superseding
the periscope as the main method of finding ships, and the only means of
detecting other submarines. With such equipment, a nuclear-powered submarine
could move wherever it chose, perhaps 200 metres or more below the surface,
at whatever depth was best for listening. It did not need to ‘come shallow’
unless the captain wanted to look through the periscope or use the electronic
sensors on periscopic masts to intercept the enemy’s transmissions.

A further aid to underwater concealment, for non-nuclear submarines,
was the provision of high-capacity batteries and powerful engines to recharge
them quickly. The quietest form of propulsion is an electric motor, although
a modern nuclear plant can be very quiet with the help of sound-insulation
and other techniques. Electric motors, however, have one serious drawback:
the storage batteries that supply them are drained in an hour or two at
top speed and in two or three days at an economical speed of, say, 3 knots.
That is why submarines have to use either diesel propulsion, and ‘snorkelling’,
or, which is far better and much faster, nuclear propulsion for prolonged
running.

These technical developments have produced three types of submarine
that appear to dominate maritime strategy. There are nuclear submarines
armed with ballistic missiles (SSBNs), which can remain underwater for weeks
or even months. Their purpose is to avoid detection while presenting a nuclear
deterrent. Then there are the nuclear-propelled attack submarines (SSNs),
which are the ‘hunter-killers’ of enemy ships and submarines. These can
also stay submerged, at high speeds if necessary, for a time that is limited
only by the endurance of their crews. The third type, the diesel-electric
patrol boats (SSKs), never have to surface at sea but they do expose a snorkel
tube periodically to gulp air for the greedy diesel engines. The snorkel
is now a dangerous giveaway to enemy aircraft, although an SSK would hope
to detect an aircraft’s searching radar and pull the snorkel down before
being found itself. Snorkelling is also quite noisy and liable to be heard
by enemy submarines. Another problem with snorkelling is that an SSK’s own
sonar is apt to suffer interference from the noise created. A submarine’s
sonar is also less efficient at the shallow depths necessary for snorkelling.

As developments in propulsion and weaponry have continued, submarines
have tended to become bigger and more expensive. Naval architects have always
had to measure the payoff between size and cost. Big submarines can, in
general, go faster and farther than smaller ones and they can also carry
more weapons. But they cost a lot more. A British Trafalgar class submarine,
a hunter-killer SSN, displaces 5208 tons when submerged. It costs about
pounds 200 million to build. The US Navy’s 9100-ton Seawolf SSN, due to
enter service in 1995, is quoted at three or four times that cost.

Big and not so beautiful

The escalating price of submarines is not just a Western problem. The
Soviet Alfa-class of submarine, which weighs in at a relatively modest 3700
tons, is capable of diving to a record 700 metres and racing at a record
45 knots. It became known as ‘golden fish’ in Russian circles because the
boat is built from an expensive material, titanium alloy, and because of
its two liquid-metal reactors, which have a novel design.

There are also operational problems with the trend towards bigger and,
therefore, more powerful submarines. In shallow or confined waters, where
a good many future submerged encounters are likely to take place, their
usefulness is wasted, and they may be at risk. Indeed, there are other situations
where it is a positive disadvantage to be big.

For instance, the primary task of a hunter-killer SSN is to track and,
in war, to destroy its own kind, and for that it needs to be quiet. But
with underwater opponents becoming equally quiet, the chance of hearing
them on purely passive, or listening, sonar at any respectable range is
diminishing. It may be, therefore, that a hunter-killer submarine will sometimes
be forced to use active sonar, great blasts of low-frequency noise that
‘illuminate’ a hostile vessel and reveal its position by echoes reflected
from the hull. For this reason, SSNs have hulls coated with thick, absorbent
material to reduce reflectivity. Anechoic tiles do not confer sonic ‘invisibility’,
however; they only lessen the possibility of being detected by active means.

Meanwhile, the problem is that active sonar reveals the searcher, and
the hunter-killer then abandons the very stealth that it has taken such
pains to acquire. Of course, the enemy commander may well respond by ‘going
active’ as well, especially if he also hears the telltale sounds of a submarine
preparing to shoot: the opening of torpedo-tube bow caps or, at the last
moment, the faint noise of a weapon being discharged. At this point the
hunter may regret being quite so big because by now the two antagonists
will be only a few kilometres away from each other and the enemy’s acoustic
‘searchlight’ may enable a swift counterattack. In these increasingly likely
circumstances, a little submarine is more likely to get away with it than
a leviathan.

In addition, big submarines are more likely to emit other signatures
that an enemy can detect. Special sensors, usually airborne, can, for instance,
measure variances in sea temperature due to the thermal wake created by
a submarine, known as thermal scarring. Other sensors can also discern the
turbulence and water displacement caused by a large submarine making its
way through the depths below. Sensors can also reveal anomalies in the Earth’s
magnetic field caused by a metallic object moving in the ocean: the more
massive the object, the greater the magnetic disturbance. Biological luminescence
(the emission of light from marine microorganisms when the water is disturbed)
and the discharge of contaminants are further potential indicators of a
submarine’s presence. Again, the bigger the boat, the more obvious they
are.

Big, then, is becoming less beautiful in submarine warfare. There could
be advantages in having more, smaller boats, which would be cheaper, provided
they had adequate weapons and propulsion systems that did not unduly restrict
their operations. But the twin requisites of speed and endurance require
a lot of space in the hull when using traditional methods of propulsion,
whether diesel-electric or nuclear.

There are other factors to be considered for lengthy patrols. Endurance
implies a choice of weapons, with enough reloads, to meet changing circumstances.
It takes quite bulky equipment to control the submarine, its sensors and
its weapons. The crew needs comfort, purified air, provisions and fresh
water. A reasonably dry atmosphere is essential for electrical and electronic
equipment. Standby machinery and spare parts must be carried in case things
go wrong.

All these requirements, especially for propulsion and weaponry, add
up to a big, fat and expensive submarine. But could submarines really become
smaller without becoming significantly less effective or, perhaps, could
greater numbers of cheaper boats compensate for fewer weapons in any one
hull? Above all, is there a viable alternative to nuclear power with its
space-consuming machinery and heavy shielding against ionising radiation?

Three countries in particular, West Germany, Sweden and Italy, have
investigated a number of possibilities. The common aim is to find a propulsion
system that does not need to take in oxygen from the atmosphere and that
will perform as well as a nuclear reactor or, at least, markedly improve
on the electric motor with its total dependence on storage batteries.

The Swedish government has developed the Stirling anaerobic engine,
which differs from a conventional engine in that heat is supplied externally
and continuously to a working gas in a closed system. A regenerator reclaims
energy by supplying back to the cycle much of the heat contained in the
gas after expansion. The engine is supplied with liquid oxygen carried in
tanks. A 1000-ton submarine would need two Stirling generators, each pumping
out 70 kilowatts of power, to cater for the electrical load at slow or moderate
speeds while allowing standard batteries to remain charged and available
for short sprints.

Another alternative for propulsion that does not need air is the fuel
cell, which combines oxygen and hydrogen to reproduce electricity directly.
One type of fuel cell, which is believed to be capable of driving a submarine
at 7 or 8 knots for several days, has been installed experimentally in the
West German boat U-1. Hydrogen and oxygen are fed to two electrodes, where
one of the gases yields up electrons and the other takes them up. The electrons
flow in a circuit, so producing an electrical current to supply the motor
and auxiliaries. The waste product is water, which can be discharged to
sea. As with the Stirling system, a battery provides the necessary power
for short, fast bursts.

Unfortunately, neither the Stirling nor the fuel cell promises a performance
anywhere near to that of a nuclear plant, which can sustain speeds of around
30 knots indefinitely. Over the past few years, however, Italian engineers
have developed an alternative that promises to rival, eventually, the performance
of a nuclear plant for most tactical purposes. It could amount to another
revolution in submarine design.

It all began in the early 1970s, when Giunio Santi, now vice president
of Maritalia, an Italian defence company, set himself the task of devising
a non-nuclear propulsion system. He began with midget submarines, which
are mere specks in the sea, displacing 0.5 per cent of the weight of a hunter-killer
SSN. Santi wanted a high-performance craft whose engine did not need to
take in oxygen from the air. He decided that chemical energy was perfectly
capable of providing any desired performance, as long as there was enough
space for storing the energy. There, as always, lay the problem.

Santi hit upon a new, yet simple idea. If he could construct a submarine
from a series of circular pipes, or toroids, rather than steel plates –
like a Michelin man lying on his side – the prime energy source, specifically
gaseous oxygen at the very high pressure of around 35,000 kilonewtons per
square metre, or 350 atmospheres, could be stored in the hull itself. This
oxygen could be combined with fuel oil for an ordinary diesel engine converted
to close-circuit running. Santi believed that the exhaust gases could be
scrubbed, neutralised and stored, rather than being ejected into the sea.
This would overcome the problem of forcing out gases underwater against
external pressure. Also, by storing these gases, there would be no warm
exhaust wake or contaminants to give away the submarine’s presence.

Santi called his integrated system GST – gaseous storage in a toroidal
hull. No snorkel is needed, but a modest battery is included in the design
for ultra-quiet running in difficult situations and ‘just in case’. A bonus
was to come. Trials on a test toroidal hull confirmed that it was, weight
for weight, five times as strong as its equivalent made from steel plates.
Furthermore, this method of building the ideal teardrop form for a submarine
was easier than bending thick sheet metal in two planes.

Another great advantage is that a GST midget has more than three times
as much usable internal space as a diesel-battery craft – 80 per cent against
25 per cent. Presumably, this means that bigger GST boats would have more
space for weapons and equipment than conventionally designed boats. The
GST system should enable submarines to be smaller.

The concept of GST has been well demonstrated in prototypes, by an engine
running for 25,000 hours underwater, and by the first operational military
midget, which commenced trials at sea last year. In February 1987, the Italian
Chief of Naval Operations, Admiral Giasone Piccioni, said that Maritalia’s
technology would be suitable for Italy’s navy. The first military midget
using GST technology is called ‘3GST9’. The three in the name specifies
the outside diameter of the toroids, 3 inches (pipe diameters are still
measured in imperial units), and the nine indicates the submarine’s length,
in the range of 9 to 9.99 metres.

The GST midget is primarily intended to penetrate enemy harbours and
destroy the enemy at home. The tiny but powerful craft is 9.65 metres long,
teardrop in shape, and displaces 29 tons. Its main weapons are ground or
limpet mines but it can take miniature torpedoes to defend its own territory
against, for instance, hostile swimmers. An exit and re-entry chamber allows
divers to come and go at will. The midget has a range of about 200 nautical
miles at 6 knots or 100 nautical miles at 8 knots while fully submerged
and working on a closed-circuit diesel engine. It can dive below 400 metres.

This performance is an enormous improvement over the 30-ton X-craft
midgets that Britain used in the Second World War. Underwater, these small
submersibles could last less than 1 hour at their maximum speed of 6 knots,
and they could scarcely remain fully submerged on electric propulsion for
24 hours at an economical 2 or 3 knots. They could go no deeper than 100
metres. Yet those same X-craft achieved astonishing successes during the
war: in September 1943, two of them, each crewed by four men, crippled the
42,000-ton German battleship Tirpitz 80 kilometres up a Norwegian fjord
behind supposedly impregnable defences. This triumph released, for urgent
duties in distant waters, two American battleships and heavy units of the
Royal Navy’s Home Fleet, all guarding against the possibility of the ‘Beast’,
as Winston Churchill called the Tirpitz, emerging to savage convoys on their
way to Murmansk.

Maritalia is now working on larger GST mini-submarines and is believed
to be building one at Milan. These mini-subs displace up to 150 tons and
are 23 to 27 metres long. They carry torpedoes or a panoply of other weaponry,
including ground mines, mine-delivery vehicles, swimmer-delivery vehicles
(tiny canoe-like submersibles), limpet mines or a team of 16 commandos.
Such mini-submarines will be able to cover the Mediterranean and Adriatic
seas from an Italian base. One version will have a burst speed of 25 knots,
a top cruising speed of 16 knots and a range of 2000 nautical miles at 8
knots without having to come near the surface.

Mini-submarines built on the GST principle cost around pounds 22 million,
which is within the price range of several foreign navies. No special infrastructure
is required apart from a plant to produce pressurised oxygen, and the training
for the boat’s engineers takes only a couple of months. The cheapness of
the submarines, the difficulty in detecting these much smaller targets and
the ease with which crews can be trained, should make them extremely attractive
to the poorer navies. A number of Western naval experts have already pointed
to the danger they pose if they fall into hostile hands.

Maritalia has yet to demonstrate in practice that GST technology can
be adapted to medium-sized boats, up to 2800 tons. If it can, and if the
performance is on a par with nuclear-propelled submarines, then this new
technology could complement, or even challenge, the large nuclear hunter-killers
that are currently deemed, by submariners at least, to rule the seas from
below.

Richard Compton-Hall is director of the Royal Navy Submarine Museum,
Gosport, England, and a former commander of submarines for the Royal Navy.
He has written seven books and numerous articles on underwater warfare.