The incursion of a Chinese nuclear-powered submarine into Japanese territorial waters this month has illuminated a mounting competition under the surface of the Pacific and Indian Oceans and their adjacent seas.
The chief rivals for submarine supremacy in this region are China, which has given priority to submarines as it acquires a blue-water or deep-sea navy, and the US, which is rebuilding submarine capabilities that had atrophied after the Cold War.
China and the US are not alone. North Korea has a sizeable coastal submarine force and South Korea has begun to counter it. Japan has a modest but proficient fleet.
Taiwan is pondering the procurement of eight boats that would triple the size of its force. The city-state of Singapore has three submarines and is acquiring a fourth. Australia has six modern submarines, based on a Swedish design, for surveillance in the Pacific and Indian Oceans.
In South Asia, India has been acquiring a submarine fleet with Russian help. A specialist on South Asia, Donald Berlin of the Asia-Pacific Center for Security Studies in Hawaii, has written that India will also build six to twelve French-designed submarines and is working on a nuclear-powered boat that will go to sea in 2006.
Pakistan has launched two submarines and is constructing a third. Berlin says "Pakistan will likely want a submarine-based nuclear weapons delivery system" to deter India. Iran has several submarines.
Even Israel, usually considered a Mediterranean nation, is believed to have sent submarines armed with cruise missiles through the Red Sea into the Indian Ocean to deter a potential nuclear attack by Iran.
In contrast, Russia, which once deployed 90 submarines into the Pacific, has laid up all but 20 boats because of that nation's financial distress.
"They've held onto their more capable boats," said a US official with access to intelligence reports, but their operations are constricted.
The Chinese submarine in Japanese waters was one of five Han class boats, the first of China's nuclear-powered submarines. After she left port at Ningbo, she was detected by Taiwan as she steamed east, then by the US near Guam in the central Pacific, and finally by Japan after she turned north to steam near Okinawa.
After a Japanese protest, Chinese spokesmen expressed regrets and blamed the mistake on unexplained "technical difficulties," raising questions about Chinese seamanship; the Chinese have long had problems operating submarines.
China is acquiring submarines to "patrol the littorals, blockade the Taiwan Strait, and stalk [US] aircraft carriers," say two researchers, Lyle Goldstein and Bill Murray, at the Naval War College in Rhode Island.
China, which has 50 submarines in two older classes, began expanding 10 years ago when it bought four Russian "Kilo" submarines, then ordered eight more in 2002 for delivery starting next year.
The Chinese are producing the "Song" class of attack boats armed with cruise missiles. Training has been intensified throughout the fleet.
It is in the Taiwan Strait that Chinese and US submarines would most likely clash if China seeks to blockade or invade Taiwan, the country over which it claims sovereignty but whose people prefer to remain separate.
US submarines would go into action because Taiwan lacks sufficient anti-submarine weapons to break a blockade or stop an invasion. The US policy is to help defend Taiwan from an unprovoked assault by China.