The US military is planning a long-term program to bolster South Korea's naval defenses after the sinking of a South Korean warship, allegedly by North Korea, The New York Times reported on Monday.
The newspaper said the March 26 incident revealed that years of spending and training had still left the country vulnerable to surprise attacks.
A torpedo attack on the 1,200-tonne Cheonan corvette killed 46 South Korean sailors. International investigators reported on May 20 their conclusion that a North Korean submarine had fired the torpedo to sink the warship.
The North has denied involvement and responded to the South's reprisals with threats of war.
It has cut all ties with the South, scrapped pacts aimed at averting accidental flare-ups along their disputed sea border and vowed to attack any intruding ships.
In an interview with The Times last week, Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, said a planned joint training exercise with South Korea planned just off the country's coast represented only the "near-term piece" of a larger strategy.
The longer-range effort would be finding ways to detect, track and counter the miniature submarines, which he called "a very difficult technical, tactical problem," he added.
"Longer term, it is a skill set that we are going to continue to press on," he told the paper.
That would involve greatly expanding South Korea's anti-submarine network to cover vast stretches of water previously thought to be too shallow to warrant monitoring closely -- with sonar and air patrols, for instance, the report said.
It would include costly investment in new technologies, as well as significant time spent determining new techniques for the South Korean military, The Times noted.