U.S. military bases in Japan are stepping up activity as the United States prepares to retaliate for the devastating terrorist attacks last week in New York and Washington.

The guided-missile destroyer USS Curtis Wilbur deaprts from Yokosuka naval base.

At 8:30 a.m. Monday, the 8,422-ton, guided-missile destroyer USS Curtis Wilbur left the naval base in Yokosuka, Kanagawa Prefecture. About 30 minutes later, the 9,407-ton guided-missile cruiser Vincennes put out to sea.

The Foreign Ministry said the 6,082-ton, nuclear-powered submarine USS Bremerton would anchor for a short time at Yokosuka.

It is believed the sub will take part in joint exercises with the Curtis Wilbur and Vincennes.

The guided-missile cruiser USS Cowpens, carrying Tomahawk cruise missiles, left Yokosuka on Saturday, becoming the first U.S. naval vessel to leave the base since the terrorist attacks.

The 9,957-ton, Ticonderoga-class Cowpens is equipped with the Aegis air defense system, which allows simultaneous attacks on multiple targets. U.S. Navy officials, however, declined to disclose the warship's mission or its destination.

Japanese employees at the base in charge of maintenance and supply for warships worked over the weekend to prepare for the departure of other vessels.

Warships at Yokosuka can reach the Indian Ocean or the Middle East in one week.

Planes from the aircraft carrier USS Kitty Hawk carried out drills until late at night over the weekend at the U.S. Navy's Atsugi Naval Air Facility, also in Kanagawa Prefecture.

No prior notice of the training was sent to Yamato and other municipalities around the base, and base officials declined comment.

At Kadena Air Base in Okinawa, the largest U.S. Air Force base in East Asia, the atmosphere was tense.

Immediately after the attacks, servicemen shouted at Japanese photographers taking pictures of the base, pointing rifles at them.

Six warplanes and two tanker planes left Kadena for Alaska on Sunday morning for midair refueling drills.