April 6 (UPI) — The United States and South Korea began a joint investigation Monday to locate the wreckage of at least three U.S. aircraft that crashed off South Korea’s northeastern coast during the Korean War, officials said.

The four-week survey of the Gangneung and Yangyang areas of northeastern Gangwon Province seeks to trace the wreckage of a fighter plane and two transport aircraft, ahead of underwater investigations scheduled for August, South Korea’s Ministry of Defense said in a statement.

The joint survey is being conducted by the Pentagon’s POW/MIA Accounting Agency and South Korea’s Ministry of National Defense Agency for KIA Recovery and Identification, which will collect materials, including information from local residents, as well as confirm the availability of medical decompression chamber facilities essential for underwater operations.

“Since 2024, I have been coming to Korea for three years to work with MAKRI to find traces of the heroes who fought in the war,” U.S. Marine Staff Sgt. Jordyn King, deputy team leader of the Pentagon’s DPAA investigation team in South Korea, said in a statement.

“During the one month given to us, we will carefully gather materials so that we can achieve good results in the future underwater investigation.”

Seoul said the survey covers three aircraft crash sites, including that of a transport plane that crashed on Nov. 15, 1952, after departing Gangneung Air Base for Pohang with nine people, including a South Korean service member, on board.

The plane suffered engine trouble mid-flight and crashed into the sea.

A second site is waters near Yangyang County, where a U.S. aircraft crashed on Feb. 21, 1952. The third is in waters near Gangneung, where a transport plane with 17 people on board crashed on Oct. 16 of that same year after suffering a mechanical problem.

“Just as we recover the remains of South Korean troops killed in action, we will spare no support in helping to find the war dead and missing of the U.S. military who helped us,” Lt. Col. Kim Seong-hwan, acting head of MAKRI, said in a statement.

The announcement comes months after the two agencies signed a memorandum of understanding in Arlington, Va., committing to the recovery and identification of remains of soldiers who were classified as missing during the Korean War of 1950-1953, which ended with an armistice.

According to a DPAA release announcing the signing in August, the agreement enhances cooperation and collaboration between the two agencies, while streamlining efforts to locate, excavate and identify the remains of fallen service members.

More than 1.8 million Americans served in the Korean War of 1950-1953, about 37,000 of whom were killed, more than 92,000 wounded and roughly 8,000 were listed as missing, according to Pentagon statistics.