The Navy ship USNS Salvor, which hadn’t been out to the wreck site of two crashed Marine Corps CH-53E Super Stallions since last month due to high seas, left Pearl Harbor this afternoon under calmer conditions to begin recovery operations, the Marines said today.

Twelve Marines with Marine Heavy Helicopter Squadron 463 and Marine Aircraft Group 24 at Kaneohe Bay went down in the two choppers the night of Jan. 14 about two miles off Waimea Bay during routine flight training. Witnesses reported seeing a fireball at sea. No Mayday call for help was made.

The search and rescue operation transitioned to recovery and salvage on Jan. 19. The status of the Marines changed to “deceased” on Jan. 20 after five full days of searching.

The Salvor had not returned to the debris site since the end of search and rescue operations, said Capt. Tim Irish, a Marine Corps spokesman. The Salvor headed out at 4 p.m. today, Irish said.

Military crews worked on detailed mapping of the debris field, mission planning, and delivery of equipment aboard the Salvor in preparation for better sea states. The operation may take weeks to complete and weather conditions may temporarily halt recovery efforts, Irish said.

The size of the debris field is several square miles at varying depths greater than 300 feet, he said.

U.S. Navy deep dive equipment will be used for recovery. “This is an underwater remotely operated vehicle with sophisticated recovery capabilities,” Irish said.

A Coast Guard-enforced temporary safety zone remains in effect surrounding the area where the Salvor will operate.

The Marine Corps said on Feb. 2 that none of the 12 Marines had been recovered. Capt. Cassandra Gesecki, a spokeswoman for the III Marine Expeditionary Force, said at the time that “trace elements of remains, in the form of DNA, were recovered during the search and rescue phase that ended on 19 Jan.”

“The families of the Marines that were identified have been informed of this information,” Gesecki said.

The plan was as the sea state permitted, Salvor and the Navy’s Mobile Diving and Salvage Unit 1 were to continue to use remotely operated vehicles to search, assess and survey the accident site to further identify and map the debris field, Gesecki said.

“This data will assist with recovery efforts,” she said, adding that such operations “can take several months to complete.”

The Navy Personnel Command said Navy divers perform ocean, harbor and combat/expeditionary salvage operations in up to 300 feet of water. The 255-foot Salvor has a crane that could pull the aircraft out of the water, said the ship’s operator, the Navy’s Military Sealift Command.

Minor pieces of aircraft debris have been recovered, Irish said. “All debris recovered thus far was either recovered floating on the surface by the U.S. Coast Guard during active search and rescue operations or it is debris that has washed ashore,” he said.

He added that any depth in an open ocean austere environment greatly complicates recovery and salvage, but diving operations have multiple courses of action to deploy various assets.

“Ultimately, safety to personnel and risk to mission decides which diving capability will be used.” Irish said. “There are many factors involved, such as the amount of personnel to support diving operations, inclement weather, support equipment available, ship organic equipment for recovery and salvage, and mooring systems. Salvage diving is an inherently dangerous and complicated operation at any depth.”