Just off the coast of California a hunt is underway.
American cruisers and the USS Ronald Reagan aircraft carrier ply the deep Pacific waters,
and underneath a Los Angeles class nuclear attack submarine prowls for its quarry.
Overhead, anti-submarine warfare helicopters buzz around the carrier battle group, routinely
stopping to dip their hanging sonar into the water and listen for the sub everyone is hunting
for.
Poseidon aircraft fly overhead, their powerful magnetic anomaly sensors scouring the sea
beneath the big planes.
Thousands of eyes are glued to electronic screens, or scouring the sea with binoculars.
Just three miles away from the mighty USS Ronald Reagan, a slender periscope breaks
the surface.
It snaps four photos of the big aircraft carrier, and then sinks once more beneath the waves.
It's mission has been achieved, the tiny Swedish submarine has successfully penetrated all
the various layers of American anti-submarine defense and scored a simulated hit on the
Ronald Reagan.
This wargame occurred in 2005, after the US Navy struck a deal with Sweden to lease the
submarine and her crew for participation in major anti-submarine warfare war games.
If the scenario had been a real war time condition, the small Gotland class submarine would have
definitely scored hits on the Ronald Reagan, though with her relatively small torpedoes
and limited number of launch tubes, it's unlikely the massive Reagan would have been sunk or
even declared a mission kill.
Still, when you're operating the world's largest supercarriers, and each carrier is home to
more firepower than many country's entire air forces, you don't want to be taking unnecessary
risks.
The bigger question however is how did this small Swedish sub even manage to penetrate
through the many rings of security supposed to protect the most powerful warships in the
world?
Immediately after the end of World War II, a fierce debate over the future of American
firepower erupted at the highest levels of military leadership.
The US Navy insisted that big aircraft carriers were the best tools for projecting American
firepower, while the newly created Air Force insisted that its B-36 long range bomber program
was in fact the best fit.
After many hearings, Congress eventually sided with the Air Force, and a planned expansion
of aircraft carriers was cancelled.
However during the Korean War the close air support made available by aircraft carrier
assets convinced the country that aircraft carriers were indeed a critical way of projecting
power forward, and a new emphasis on their construction began.
As the Cold War evolved, the Soviet Union greatly feared the growing threat of American
carriers.
Once the US developed nuclear weapons small enough to be equipped by carrier-based planes,
those fears were intensified.
This led them to aggressively pursue the use of nuclear submarines in order to hunt and
kill American carriers in the event of war.
The US was well aware of this threat, and its intelligence on Soviet submarines was
far better than the Soviet Union ever truly knew.
Thus America quickly developed the most robust anti-submarine warfare capability in the world,
and the US was so confident it could defeat Soviet subs, that aircraft carriers played
prominent roles in war plan offensives against the Soviet Union.
When the Cold War ended though, the US Navy found itself armed to the teeth for a war
that never came, and with no significant opponent that could match the level of readiness the
Soviet Union had forced the US Navy to maintain.
China was a growing problem, but its navy was- and remains today- decades behind in
capabilities to the US, and its own submarines are so notoriously loud that sonar operators
have described Chinese subs as “washing machines being dragged behind a pick-up truck
down a gravel road”.
With no significant threat to American carriers, the US's anti-submarine warfare capabilities
began to atrophy, and this only worsened with the retirement of the S-3 Viking patrol aircraft
and the Oliver Hazard Perry class of frigates, both key tools in the Cold War navy's anti-submarine
warfare toolkit.
To make matters worse, the launch of the dual wars in Iraq and Afghanistan saw the Navy
shift its focus from blue water naval operations, to coastal support roles, lending their surface
and undersea firepower to land units in need of fire support.
Budgets, and technology, were invested in giving Navy vessels improved ability to target
and destroy land targets and better support ongoing shore-based operations.
Under the waves though, the American sub fleet was being slowly neglected, and it wouldn't
be until President Obama's second term that a big investment in submarine purchases would
see a growing gap in available vessels finally start to shrink.
By 2005 it was growing increasingly obvious that China wasn't content to let the current
balance of power in the South Pacific rest as it had for decades, and its aggressive
and illegal seizure of maritime territory belonging to its neighbors proved to the US
that China could very quickly become the US Navy's public enemy number one.
While Chinese submarines were decades behind in stealth technology, many international
ship builders were starting to produce new models of diesel-electric submarines that
could threaten America's big carriers.
Despite these threats, the US Navy had allowed its anti-submarine warfare capabilities atrophy
to disastrous levels.
It was time to make a change.
First though, the Navy had to determine what kind of a threat these new Air Independent
diesel-electric submarines posed to modern carriers.
A relatively new development, air independent diesel-electric subs bridge the endurance
gap between nuclear submarines and traditional diesel subs.
Nuclear submarines are notoriously difficult to run silently, and the US Navy has spent
billions on research into quieting the many very noisy systems that keep a nuclear reactor
running smoothly.
The constant need for water as coolant to be pumped into the reactor for instance is
one hurdle that the US Navy has long cleared, but navies such as Russia's own never quite
did.
China, for all intents and purposes, never even made it out of the starting block in
this regard.
By comparison though, a diesel electric submarine runs perfectly silent when it is under water.
That's because these subs use air-breathing diesel engines while on the surface of the
ocean to charge massive banks of batteries, and then turn their engines off and cruise
the depths on battery power alone, completely eliminating all the potential noise of a nuclear
sub.
Yet this ability comes with the obvious drawback that a diesel sub will very quickly have to
resurface in order to run its engines and replenish its batteries, and this has traditionally
limited the endurance of diesel subs to just days.
A new development in diesel submarines though has resulted in what is known as 'air independent'
propulsion systems, in which the diesel engines can still be run even while under water.
Typically liquid oxygen is mixed with an inert gas and pumped into the engines so that they
can burn the diesel as fuel, and then waste gases are vented into the ocean.
Thus this new generation of diesel subs can recharge their batteries while underwater,
and not give themselves away by having to surface every two to three days.
An AIP diesel sub can have an endurance of up to two weeks, which is far and away better
than any other diesel submarine to date.
This increased endurance has made diesel submarines a threat to ships operating in deep waters,
as in the past there was little threat from diesel subs getting anywhere near the depths
that an aircraft carrier might operate from, as they simply didn't have the endurance.
Now AIP diesel subs offer a cheap alternative to nations wishing to build a fleet capable
of striking in deep waters, with an AIP diesel sub running anywhere from $100 to $500 million
dollars, or about a quarter the price of a nuclear submarine.
In 2005 the US got to see for itself just how effective these small, lethal boats were,
and though details of the war games remain classified, it is rumored that the Gotland
and its Swedish crew managed to score many hits and even some kills on US vessels during
the one year it was on lease to the US.
In fact the United States went so far as to lease the sub and its crew for an additional
year, as it carefully studied the capabilities of the sub and developed strategies to defeat
this new generation of quiet, stealthy diesel-electric subs.
The result of the two years of war games was an increased focus on America's seriously
flagging anti-submarine warfare capabilities, and the development of new tools such as autonomous
sub-hunting drone ships now in active duty service.
With the threat of a possible conflict with China in the South China Sea, the US Navy
is no longer taking any chances in the realm of undersea warfare, and its traditional edge
in anti-submarine warfare is once more being honed.
Yet just how vulnerable are big ships such as a modern supercarrier to this new generation
of small, stealthy diesel-electric subs?
Well, even the best equipped navy in the world is going to have trouble dealing with submarines.
It is notoriously difficult to locate and track submarines beneath the waves, and thus
the best defense that a modern carrier has is to simply stay on the move at all times.
An American supercarrier has a cruising speed of about 35 knots, which is approximately
the top speed of most submarines.
By staying on the move, a sub will have a very difficult time getting close enough to
get a firing solution, or will have to burn up its fuel or energy reserves in order to
keep up.
For a nuclear powered sub this isn't a problem, but for a diesel electric submarine this poses
a huge issue, and is the reason why the US Navy has always opted for nuclear power.
Yet a diesel-electric sub such as Sweden's Gotland doesn't have to catch up with a carrier
if it can instead simply wait directly in its path.
This might be tough for a country with a small submarine fleet such as Sweden to do in a
real war, as aircraft carriers routinely make abrupt course adjustments for just this reason.
Yet a large enough group of submarines could potentially spread out over a large enough
area that the big carrier will eventually be moving in one of their directions.
With its engines powered off and resting still and silent, a submarine is practically undetectable,
and it can simply sit still and wait until it has a firing solution on the approaching
carrier, fire off its torpedoes, and then quickly make its escape.
Smaller submarines such as the Gotland and its limited number of torpedo tubes and smaller
warheads are unlikely to destroy a big supercarrier, as they would be detected immediately upon
opening fire and sunk themselves in return if they didn't flee as soon as they launched
their opening volley.
Yet larger diesel-electric subs can carry more torpedo tubes with larger warheads, and
these pose a significant threat to big surface ships.
Not impossible to detect, or defend from by any means, small, cheap diesel-electric submarines
nevertheless pose a significant threat to any surface ship, and especially so when a
navy has allowed its anti-submarine warfare training and capabilities both to atrophy.
Do you think the US Navy should invest in diesel-electric subs over the big, expensive
nuclear powered subs?
Are aircraft carriers simply too big a target to risk operating anymore?
Let us know in the comments!
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