"Sub hunters": Detecting the enemy beneath the sea

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By Luke Baker

FARNBOROUGH (Reuters) - They call themselves "sub hunters",
men and women trained to detect enemy submarines gliding in
the depths of the world's oceans.

Like Cold War spies, they use a mix of state-of-the-art
technology, rigorous training and split-second intuition to
find out where the hidden subs are, where they may be headed
and how fast they are going.

The Cold War may be long over, but the demand for the trade is
as strong as ever.

With 540 submarines in operation around the world, many in the
hands of what the British military refers to as "potential
enemies", training officers say the threat remains as real today
as it was three decades ago.

That has been underlined in recent weeks with Russian President
Vladimir Putin reviving the Soviet-era practice of sending bombers
out on long-range patrols, a move interpreted in the West as saber-
rattling by its erstwhile enemy.

"The threat now is far more diverse than it was during the Cold War,"
said Master Air Crew Steve Street, a member of the team that instructs
the top sub hunters and which last week cautiously opened its door to
the media for the first time.

The timing of this -- just days after Putin's announcement -- may be
coincidental and the nature of the threat different, but the cat-and
-mouse game between submarine and sub-hunter was as much a Cold
War feature as that between bombers and fighters.

"Even if a British ship has not been sunk since the Second World War
... the submarine threat is still incredibly significant," said Street.

To counter this, Britain's navy and air force run what's called the "A"
course, an elite training camp at a high-security compound near London
for experienced sonar operators from Britain, Australia, Canada and
other allied countries.

The month-long course, dubbed the "Top Gun" of the sonar world,
teaches up to two dozen trainees the most advanced techniques for
detecting submarines amid the cacophony of marine life and merchant
shipping emanating from the ocean depths.

Watching graphs of sonar patterns and listening to sounds captured by
underwater microphones, the trainees learn to separate merchant ships
from trawlers, the noise of whales from that of seals, the creak of
pack-ice from the screech of icebergs -- and amid it all the hum of
submarines.

What's more, a trained ear can quickly calculate not only what type of
sub is moving through the water, but how fast and in which direction.
The best can identify individual potentially hostile subs merely from
their acoustic pattern.

"We call it the 'black arts'," said Richard Horsburgh, an aural analysis
expert and "A" course trainer who spent 25 years as a sonar specialist
in the navy, including on submarines.

"It's a game of cat and mouse. You build up a database in your head so
you can identify almost anything.

"When I was in the subs during the Cold War, we'd patrol the oceans for
weeks at a time, sucking up as much acoustic information as we could
get, and then sneak off."

In such an intense occupation, recalling maritime warfare between
Britain and Germany during World War Two, it's no surprise that
teachers or students of the course are fans of the 1981 German
movie "Das Boot" --the epic tale of a U-boat crew hunting British
warships.

Training officers declined to identify the source of a perceived post
-Cold War threat, but more submarines have been sold on now by
major powers like Russia and China to countries including Venezuela
and Iran.

Russia has around 70 submarines and while patrols have declined
sharply since the mid-1980s, defense journals say they have picked
up again in recent years.

These days sub hunters still go down in Britain's 15 nuclear submarines,
but also work in coordination with the air force and its fleet of Nimrod
patrol aircraft. Surface ships and some helicopters also have sonar
operators aboard.

The hours can be long, particularly on a submarine that might not
surface for months at a time, and the work taxing.

Separating the noise of a single diesel sub, which are quieter than
nuclear submarines, from the sonic bedlam created by an ocean full
of whales, seals, icebergs, underwater landslides and cruise and
merchant ships can be nerve -racking.

"It comes down to one guy sitting at a sonar set trying to detect an
enemy submarine and if he doesn't get it right ..." said Street, the
trainer, clicking a mouse and running a video of a British frigate being
torpedoed in an exercise.

The navy sees the "A" course as the best way of building up skills to
steadily improve the chances of correctly identifying the threat that
may be out there. About 20 percent of Britain's sonar operators have
done the course.

Long before they start identifying individual submarines, however, the
first thing sonar operators learn to detect is the sound of fishing
trawlers -- no submarine captain wants the ignominy of being caught in
the net of a fishing boat.

"If you ever hear trawl noise, that's it," said Horsburgh. "Forget about
subs -- you know right then and there you have to get away."