SINGAPORE (AP) — Navies from the United States, Japan, South Korea and Singapore on Monday began the first combined submarine rescue exercise in the Pacific.

The 13-day Exercise Pacific Reach 2000 involves 600 people, four ships, four submarines and three sophisticated underwater devices that can rescue personnel from submarines in distress.

The joint exercise in the South China Sea off Singapore was planned nearly two years before the recent Russian submarine disaster that killed 118 people, but participants said the disaster heightened the importance of submarine rescue.

The Navy has begun venturing into shallower coastal waters and will use the exercise to test its shallow-water rescue capabilities, said Navy Capt. C.J. Leidig.

Russia, China, Britain, Australia, Canada, Chile and Indonesia have sent observers to the exercise.

During the exercise, some of the submarines will sit on the bottom "simulating disabled subs," Leidig said.

Underwater rescue devices such as a Navy high-tech "diving bell" will be attached to the submarines' hatches and transfer crew to the rescue vehicle. Special diving suits will also be used.

The U.S. Navy nuclear attack submarine USS Helena is taking part, along with submarines JDS Akishio of Japan, South Korea's ROKS Choi Moo Sun and Singapore's RSS Conqueror.

Japan, South Korea and Singapore are sending rescue support ships to the exercise, while the United States, Japan and South Korea are sending underwater rescue vehicles.

Japan's equivalent of a naval force is officially referred to as the Japan Maritime Self-Defense Force. Since Japan was defeated in World War II and formally renounced military aggression, its armed forces are constitutionally limited to a self-defense role.

Submarine emergencies grabbed world attention in August when Russia's Kursk nuclear submarine sank after an explosion.

Russian officials, including President Vladimir Putin, were criticized for slow and awkward handling of the incident.