File picture of USNS Yukon
An 844-foot-long US Navy assault ship collided with a refuelling tanker on Wednesday in the Pacific Ocean, causing damage to both ships, but there were no injuries or fuel spills, military officials said.
The mid-morning accident between the amphibious assault vessel USS Essex and the oiler USNS Yukon occurred about 120 miles off the coast of Southern California as the Essex was approaching the Yukon to be refuelled, said Cmdr. Charlie Brown, a spokesman for the 3rd Fleet.
Mr Brown said the steering apparently stopped working on the Essex, which was carrying 982 crew members on its way to San Diego for scheduled maintenance. It had spent the past 12 years based in Sasebo, Japan, as command ship for the Navy's Expeditionary Strike Group 7.
The Essex was traveling with a new crew that came aboard for the trip to California. The ship recently underwent a crew swap with another amphibious assault ship, the Bonhomme Richard, as part of a standard procedure in the Navy to keep its ships operating.
The Essex and Yukon were both able to continue toward San Diego despite the damage, which the Navy said did not compromise their fuel tanks or systems.
The Yukon arrived at the Navy base in San Diego after 3 pm on Wednesday with its crew of 82, including 78 civilian mariners and four military crew members.
The Essex was keeping to its planned arrival time of 9 am on Thursday.
Mr Brown said the damage was still being assessed. He said he couldn't say how fast the ships were moving at the time of the crash because the Navy is still investigating the cause.
The standard speed for ships lining up to refuel at sea is about 13 knots, or 15 mph, Mr Brown said. No lines or hoses had been connected because the two vessels were just approaching each other.
The ships likely just bounced off each other, said maritime safety consultant James W. Allen.
Even so, he said, with massive ships, it can be "a pretty hard bump that can bend metal" and cause dents. The Essex, known as the Iron Gator, resembles a small aircraft carrier, while the Yukon is 677 feet long.
Navy ships routinely refuel at sea while under way.
"They were probably so close there was no time to respond when the steering went out," said Mr Allen, who served 30 years in the Coast Guard.
Navy officials said it was the Essex's first collision. The ship, however, has had mechanical problems.
The military publication Stars and Stripes reported in February that twice over a seven-month period, missions were scrapped because of mechanical or maintenance issues involving the 21-year-old flagship commissioned in San Diego
Navy spokesman Lt. Richard Drake at the time blamed it on wear and tear. 3rd Fleet officials said they could not comment on that since at the time the Essex was in the 7th Fleet in Japan. 7th Fleet officials could not be immediately reached for comment on Wednesday.
The Yukon, which was launched in 1993, has been involved in at least two previous collisions, including on February 27, 2000, when it collided with a 135-foot civilian cargo ship while trying to enter Dubai's Jebel Ali port in the United Arab Emirates. The Yukon sustained minor damage.
Less than five months later, it was hit by the USS Denver during refuelling off the coast of Hawaii. Both ships sustained heavy damage.