The aircraft, Bureau number 135749, c/n 4316, bore the tail code “PR-21” and used the radio call sign Deep Sea 129. Aboard were 8 officers and 23 enlisted men under the command of LCDR James Overstreet. Nine of the crew, including one Marine were Naval Security Group cryptologic technicians (CTs) and linguists in Russian and Korean.

Deep Sea 129’s assigned task was a routine nationally tasked BEGGAR SHADOW signal intelligence (SIGINT) collection mission. Its flight profile northwest over the Sea of Japan took it to an area offshore of Musu Point, where the EC-121M would turn northeast toward the Soviet Union and orbit along a 120-nautical-mile (222 km) long elliptical track. These missions, while nominally under the command of SEVENTH Fleet and CINCPAC, were actually controlled operationally by the Naval Security Group detachment at NSF Kamiseya, Japan, under the direction of the National Security Agency.

LCDR Overstreet’s orders included a prohibition from approaching closer than 50 nautical miles (90 km) to the North Korean coast. VQ-1 had flown the route and orbit for two years, and the mission had been graded as being of “minimal risk.” During the first three months of 1969 nearly 200 similar missions had been flown by both Navy and U.S. Air Force reconnaissance aircraft off North Korea’s east coast without incident.

The mission was tracked by a series of security agencies within the Department of Defense that were pre-briefed on the mission, including land-based Air Force radars in Japan and South Korea. The USAF 6918th Security Squadron at Hakata Air Station, USAF 6988th Security Squadron at Yokota Air Base, and Detachment 1, 6922nd Security Wing at Osan Air Base monitored the North Korean reaction by intercepting its air defense search radar transmissions. The Army Security Agency communications interception station at Osan listened to North Korean air defense radio traffic, and the Naval Security Group at Kamiseya, which provided the seven of the nine CTs aboard Deep Sea 129, also intercepted Soviet Air Force search radars.

At 12:34 local time, roughly six hours into the mission, the Army Security Agency and radars in Korea detected the takeoff of two North Korean Air Force MiG-17s and tracked them, assuming that they were responding in some fashion to the mission of Deep Sea 129. In the meantime the EC-121 filed a scheduled activity report by radio on time at 13:00 and did not indicate anything out of the ordinary. 22 minutes later the radars lost the picture of the MiGs and did not reacquire it until 13:37, closing with Deep Sea 129 for a probable intercept.

The communications that this activity generated within the National Security network was monitored by the EC-121’s parent unit, VQ-1, which at 13:44 sent Deep Sea 129 a “Condition 3” alert by radio, indicating it might be under attack. LCDR Overstreet acknowledged the warning and complied with procedures to abort the mission and return to base. At 13:47 the radar tracks of the MiGs merged with that of Deep Sea 129, which disappeared from the radar picture two minutes later.

At first none of the agencies were alarmed, since procedures also dictated that the EC-121 rapidly descend below radar coverage, and Overstreet had not transmitted that he was under attack. However when it did not reappear within ten minutes, VQ-1 requested a scramble of two Air Force Convair F-102A Delta Dart interceptors to provide combat air patrol for the EC-121.

By 14:20 the Army Security Agency post had become increasingly concerned. It first sent a FLASH message (a high priority intelligence message to be sent within six minutes) indicating that Deep Sea 129 had disappeared, and then at 14:44, an hour after the shoot-down, sent a CRITIC (“critical intelligence”) message (the highest message priority, to be processed and sent within two minutes) to six addressees within the National Command Authority, including President Richard M. Nixon and National Security Advisor Henry Kissinger.

A search and rescue effort was immediately launched by VQ-1 using aircraft of both the U.S. Air Force and Navy. The first response was by an Air Force Lockheed HC-130 Hercules, with a Boeing KC-135A Stratotanker tanker in support and an escort of fighters, but the search effort rapidly expanded to a total of 26 aircraft. At short notice, two U.S. Navy destroyers, USS Henry W. Tucker and USS Dale, sailed from Sasebo, Japan, on the afternoon of April 15 toward the area of last contact (41°28′00″N 131°35′00″E / 41.4666667°N 131.5833333°E), a position approximately 90 nautical miles (167 km) off the North Korean port of Ch’ŏngjin.

The first debris sighting occurred at 09:30 the next morning, 16 April, by a Navy VP-40 P-3B Orion aircraft. Two destroyers of the Soviet Navy #429 Kotlin Class and #580 Kashin Class were directed to the scene by the Navy aircraft. The Air Force HC-130 SAR aircraft, that relieved the P-3B, dropped the Soviet ships URC-10 survival radios and eventually made voice contact in the afternoon as the Soviet craft were departing. Both Soviet ships indicated they had recovered debris from the aircraft but had not found any indication of survivors. That evening Tucker arrived in the area and after midnight recovered part of the aircraft perforated with shrapnel damage.

At approximately noon of 17 April Tucker recovered the first of two crewmen’s bodies, then rendezvoused with the Soviet destroyer Vdokhnovenny (D-429) and sent over her whaleboat. The Soviets turned over all of the debris they had collected. The bodies of Lt.j.g. Joseph R. Ribar and AT1 Richard E. Sweeney were taken to Japan but those of the other 29 crewmen were not recovered.

North Korea publicly announced that it had shot down the plane, claiming it had violated its territorial airspace. The U.S. government acknowledged that it was conducting a search for a missing aircraft but stated that it had explicit orders to remain at least 50 nautical miles (93 km) offshore. Of note, April 15 was the 57th birthday of the North Korean dictator Kim Il-Sung.

From WIKIPEDIA

Those lost include:

Lcdr. James H. Overstreet,
Lt. John N. Dzema,
Lt. Dennis B. Gleason,
Lt. Peter P. Perrottey,
Lt. John H. Singer,
Lt. Robert F. Taylor,
Ltjg. Joseph R. Ribar,
Ltjg. Robert J. Sykora,
Ltjg. Norman E. Wilkerson,
ADRC Marshall H. McNamara,
CTC Frederick A. Randall,
CTC Richard E. Smith,
AT1 Richard E. Sweeney,
AT1 James Leroy Roach,
CT1 John H. Potts,
ADR1 Ballard F. Conners,
AT1 Stephen C. Chartier,
AT1 Bernie J. Colgin,
ADR2 Louis F. Balderman,
ATR2 Dennis J. Horrigan,
ATN2 Richard H. Kincaid,
ATR2 Timothy H. McNeil,
CT2 Stephen J. Tesmer,
ATN3 David M. Willis,
CT3 Philip D. Sundby,
AMS3 Richard T. Prindle,
CT3 John A. Miller,
AE3 LaVerne A. Greiner,
ATN3 Gene K. Graham,
CT3 Gary R. DuCharme,
SSGT Hugh M. Lynch,(US Marine Corps).

REST IN PEACE