YOKOSUKA NAVAL BASE, Japan — More ships — including one from Japan — were called to the growing search for a 19-year-old U.S. Navy airman who fell off the USS Kitty Hawk aircraft carrier’s flight deck last weekend.

The search, which was in its fourth day Tuesday, covered 2,400 square miles of the Pacific Ocean, according to Kitty Hawk Strike Group spokesman Lt. Cmdr. John Bernard. The area expands every minute that Airman Jason J. Doyle is missing due to variables such as water current and winds, Bernard said.

The Japanese Maritime Self-Defense Force dispatched the JDS Hatakaze to help with the effort. With the addition of USNS Flint, the ships searching for Doyle now include Kitty Hawk, USS Cowpens, USS Russell, USS Lassen and USNS Tippecanoe as well as the strike group’s SH-60 helicopters and E-2 Hawkeye and P-3 Orion maritime patrol aircraft from Misawa, Japan.

The “U.S. Navy is extremely grateful for the assistance they have provided,” Bernard said. “As far as when the search will end, we don’t speculate, so it’s ongoing.”

According to the Navy, Doyle fell approximately 60 feet into the sea around 5 p.m. Saturday during routine flight operations off the east coast of Japan.

Doyle works on the flight deck, maintaining and inspecting planes for Electronic Attack Squadron VAQ-136’s Line Division.

He vanished from sight as soon as he fel,l so rescue swimmers did not go into the water, Bernard said. Doyle was wearing a “float coat” life preserver and cranial helmet, a requirement during flight operations, Bernard said.

Battle Force 7th Fleet, under Rear Adm. Doug McClain, is investigating the cause of the fall, he said.

Bernard said Doyle, who is single, was born in Leyton, Utah, and lists Omaha, Neb., as his home of record.