The U.S. Navy
has been secretive about how effective it has become in detecting
non-nuclear submarines. That discretion is necessary to prevent the
enemy from fixing any vulnerabilities you are exploiting. The quietness
of modern diesel-electric boats puts nuclear subs and surface ships at a
serious disadvantage, especially in coastal waters. This is a big
problem for the United States, which went to an all nuclear submarine
fleet half a century ago. While the nuclear sub is the most effective
high seas vessel, especially if you have worldwide responsibilities and
these nukes would have to quickly move long distances to get to the
troubled waters, the diesel electric boat, operating on batteries in
coastal waters, is quieter and harder to find.
For over a decade the U.S. Navy has been trying to get an idea
of just how bad the threat is and developing technologies and tactics
to deal with it. This was part of a larger ASW (anti-submarine warfare)
effort that began in the 1990s to deal with post-Cold War submarine
threat. A major part of this effort using a state-of-the-art non-nuclear
subs to practice on. Thus from 2005 to 2007 the United States leased a
Swedish sub (Sweden only has five subs in service) and its crew, to help
American anti-submarine forces get a better idea of what they were up
against. This Swedish boat was a "worst case" scenario, an approach that
is preferred for training. The Gotland class Swedish subs involved are
small (1,500 tons, 64.5 meters/200 feet long) and have a crew of only
25. The Gotland was based in San Diego, along with three dozen civilian
technicians to help with maintenance.
For many years before the Gotland arrived, the U.S. Navy had
trained against Australian diesel-electric subs and often came out
second. The Gotland has one advantage over the Australian boats because
of its AIP (Air-Independent Propulsion) system (which allows it to stay
under water, silently, for several weeks at a time). Thus the Gotland
was something of a worst case in terms of what American surface ships
and submarines might have to face in a future naval war. Since the
Gotland experiments the U.S. has borrowed other AIP subs for further
work in refining detection methods. None of America's most likely naval
opponents (China, North Korea, or Iran) only China has built some AIP
boats yet. These three nations have plenty of diesel-electric subs
which, in the hands of skilled crews, can be pretty deadly. China is
making an effort to create experienced and well trained crews.
Based on the experience with Australian, Swedish, German and
other subs, the U.S. Navy has been developing new anti-submarine tactics
and equipment. All this is done in secret, obviously. But apparently
the modern, quiet diesel electric boats continue to be a major threat to
U.S. surface warships and subs. Meanwhile, potential enemies build more
of their cheaper and higher quality diesel-electric boats and train
their crews by having them stalk actual warships (including U.S. ones).
The subs are getting more numerous, while U.S. defenses are limping
along because of the sheer technical problems of finding quiet
diesel-electric boats in coastal waters.
The U.S. has found that, given current sensor (sonar,
magnetic, heat, chemical) technology it is possible to detect very quiet
diesel-electric and AIP subs. To do this required many small tweaks to
existing sensors. AIP boats, in particular, were found to have many
vulnerabilities. The AIP technology generated more noise and heat than
just using batteries. The more the U.S. studied AIP subs in operation
the more ways they found these subs could be detected. It is known that
the passive (listen only) sonar systems in the new Virginia class SSNs
(nuclear attack sub) was tweaked to better find diesel-electric and AIP
boats.
Despite keeping most of the details secret, some potential
targets of these new ASW capabilities realized the danger they were in.
One reason China wants to keep American naval forces out of their
economic zone (370 kilometers from the coast, an area which does not bar
foreign warships) is so that Chinese diesel electric subs can train
without being stalked by American subs, surface ships, and aircraft
looking for realistic practice tracking Chinese boats. At the same time
the U.S. Navy has lost the full use of its most effective underwater
anti-submarine training area (a well mapped and instrumented area off
southern California) because environmentalist activists have convinced
judges that the use of active sonar in this training area is harmful to
some species of aquatic animals. So going after potential targets off
their coasts is more important than ever.
There are 39 nations operating a total of 400 diesel electric
subs. Only three of these nations (China, Iran, North Korea) are likely
to use their subs against the U.S. or its allies. China has fifty of
these boats, Iran has three (plus 25 much smaller mini-subs) and North
Korea has 20 (plus 50 much smaller mini-subs). So the U.S. has to worry
about 73 diesel electric subs and 75 mini-subs. But about half the full
size subs are elderly, obsolete, and noisy. The same can be said for at
least half the mini-subs. That leaves about 36 full size subs and 40
mini-subs that are a clear threat (though the older stuff can be a
threat if you get sloppy). That’s a lot of subs, and they make the East
Asian coast and the Persian Gulf dangerous places for American warships.
Moreover, the North Korean and Iranian fleets (and
governments) are in decline, while China is pouring more cash into their
armed forces. If there’s any diesel-electric boats the U.S. Navy has to
be extremely concerned about, it’s the Chinese. While China continues
to try and develop world class nuclear subs, they are also moving ahead
in creating world class diesel electric boats.
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