April 14, 1953 — Sea of Japan
9:23–11:50 p.m. A Navy P2V Neptune spy plane on an electronic intelligence (ELINT/ferret) mission over the Sea of Japan (about 200 miles southeast of Vladivostok, Russia) is paced and attacked by 10 agile and highly maneuverable UFOs. The encounter takes place with only 400 feet of distance between the aircraft and the sea. The objects make more than “70 aggressive non-firing passes” in “high-speed runs,” many just a few hundred feet directly underneath the Navy aircraft for just over an hour. The UFOs transmit Morse Code light signals (the letter “D”), an unprecedented occurrence in UFO history. The objects are tracked on radar and by the Navy’s ELINT systems (which pick up and analyze radar beams emitted from the objects) for almost two and a half hours. [Eberhart]
Blue Book: [Record card is for March 14th case but mentions this case]
Korea 1st Marine’s Summaries of the Enemy, Friendly, and Aviation Operations in Korea during the week of 16 April - 23 April 1953
Sources:
Brad Sparks, Blue Books Unknowns Catalogue, Case 958, p. 198;
Jerome Clark, The UFO Encyclopedia, 3rd Ed., pp. 53–59;
Jerome Clark, The UFO Encyclopedia, 4th Ed., pp. 73–78, 1110;
NICAP, “Two Lights Flashing Morse Code Letter ‘D’”;