SAN DIEGO - The crew of the USS Antietam departed Thursday to take the guided-missile cruiser to its new home port in Japan, and then bring the USS Cowpens -- the same type of ship -- to San Diego.

The 400 or so Cowpens crew members will run the Antietam at its new base in Yokosuka, Japan, according to the Navy. The procedure is called a "hull swap."

According to a Navy statement, the switch is part of a plan to move newer and more capable vessels to forward operating positions to bolster the defense of Japan and improve security in Asia and the Pacific Ocean.

While the Cowpens -- the vessel set to leave Japan -- is four years newer and of the same class of cruisers, the Antietam completed a major upgrade to its hull, mechanical, electrical and combat systems in April. The Cowpens has not received such improvements yet.

"My crew has worked very hard this past year preparing Antietam for turnover with Cowpens," said Capt. Robert Tortora, commanding officer of the Antietam. "The ship is more than ready. We very much look forward to delivering a mission-ready, upgraded cruiser to Seventh Fleet and bringing Cowpens back to San Diego."

The 567-foot Antietam is named for the site of a bloody Civil War battle. The Cowpens is named after a Revolutionary War battle.