1986 · North Pacific, north of Wake Island, en route to Midway

Kaiyo Maru: six hours of radar contacts north of Wake

Sourced, unconfirmed

Strength C · 5/10 · 2 independent

Evidence 1/4 · Witnesses 2/3 · Backing 2/3

Two radars, named officers and a government scientist as author; the article and the ship's log are the records that would raise it to B.

Plausibility High

Score 14 · 9 factors for, 0 against

Two radars and named crew of a government research ship tracked targets for six hours; a government scientist wrote it up and a Diet member raised it in 2024.

See the factors ↓

Unresolved

From Naganobu Mikio's 1988 account: the Kaiyo Maru tracked large unknown radar targets north of Wake Island on 21 Dec 1986 while nothing was visible under a full moon. · Illustration for uaptrail.com

When21 December 1986, 18:00–23:50 local

WhereNorth Pacific, north of Wake Island, en route to Midway

Backing2 independent

Evidencedocuments, sensor data

On the night of 21 December 1986, north of Wake Island, the Fisheries Agency research ship Kaiyo Maru tracked large unknown targets on two radars for almost six hours. One circled the ship twice and then closed from 10 to 1.5 nautical miles in seconds, roughly Mach 4; another vanished as it neared the ship while the crew heard a low sound and saw nothing under a full moon. The radar put it below 500 m and about 300 m across. The ship's oceanographer, Naganobu Mikio, wrote it up in 1988 and concluded the object was real. It came five weeks after JAL 1628's encounter over Alaska.

Evidence, in date order (2)

21 Dec 1986Two shipboard radarssensor data
both showed the targets, per the article Naganobu (1988)
Sept 1988Naganobu Mikiodocument
Fisheries Agency oceanographer's account in Science (Nikkei Science), September 1988 Mikio Naganobu

How plausible · High

Two radars and named crew of a government research ship tracked targets for six hours; a government scientist wrote it up and a Diet member raised it in 2024.

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Access The bridge crew on two radars.
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No gain sought Government research ship.
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Character record Veteran officers; a government scientist.
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Independent convergence Two radars and several crew.
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Physical traces or official reaction Radar tracks.
●○
Cost of speaking Named crew.

Plausibility weighs how well an account fits where secrecy hides the documents by design, so missing records never count against it. Strength measures what is documented. Assessed 2026-10-23.

Claims

At 18:00 a large oval return about 3 nautical miles to port, moving away.firsthandSourced, unconfirmedSasaki Yoji, chief second officer (39, 18 years at sea)

At 20:30 a large target closed from the east, circled the ship twice anticlockwise, then charged from about 10 to 1.5 nautical miles, about 3 nautical miles in 4 seconds (roughly Mach 4); a second target sat still about 10 nautical miles off. Both were gone by 22:40.firsthandSourced, unconfirmedKaiyo Maru bridge crew

At 23:10 a target closed from astern and vanished as it neared the ship; the crew heard a low sound and saw nothing under a full moon; a reddish-yellow egg-shaped light showed on the horizon for 1–2 seconds.firsthandSourced, unconfirmedMurazuka Masanobu, deckhand

Two radars and experienced operators rule out malfunction and error: a radar-reflective object invisible to the eye was present, under 500 m up and about 300 m across, flying unlike any aircraft.analysisSourced, unconfirmedMikio Naganobu

The Kaiyo Maru encounter 'should be in the records'; it may have been a U.S. weapons test in the area.Kaiyo Maru: a wandering light off the FalklandsspeculationLeadperson/yoshiharu-asakawa, Diet, 13 June 2024

Where

North Pacific, north of Wake Island, en route to Midway

25.0°N 168.0°E · region only

In The picture

They use the waterAt Shag Harbour police watched a light float on the sea where a line of lights had gone down; the boats found only a patch of foam, and navy divers found nothing. In 1986 the Japanese government research ship Kaiyo Maru held unknown targets on two radars for six hours north of Wake Island, one closing at about Mach 4…

Kaiyo Maru: six hours of radar contacts north of Wake

Evidence, in date order (2)

How plausible · High

Claims

Where

In The picture

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Sources