251 Kōkūtai (251 Air Group)
Imperial Japanese Navy Kokutai

Background
On November 1, 1942 the Imperial Japanese Navy (IJN) renamed Air Groups with three digit identifiers and the Tainan Kokutai was redesignated as the 251 Kokutai (251 Air Group).

Gekko / Irving reconnaissance
In early June 1942, the 251 Kokutai received their first three J1N1 Gekko / Irving reconnaissance aircraft from the 3rd Kokutai. These aircraft were assigned tail codes V-1, V-2 and V-3.

Night Fighter operations over Rabaul and southern Bougainville
During May 1943, the 251 Kokutai received two J1N1 Gekko (Irving) at Lakunai Airfield and were field modified as night fighters armed with upward and downward firing 20mm cannons and were flown by pilots Shigetoshi Kudo and Satoru Ono.

On May 21, 1943 J1N1 Irving piloted by Shigetoshi Kudo was the first to test the aircraft in combat and score confirmed victories. Over Rabaul, he shot down B-17E "Honi Kuu Okole" 41-9244 and B-17E 41-9011 firing only 178 rounds of ammunition. Next on June 26, 1943 Kudo shot down B-17E "Naughty But Nice" 41-2430 and B-17F "Taxpayers Pride" 41-24448. Then on June 30, 1943 shot down B-17F "Pluto" 41-24543 and possibly B-24D 42-40254.

Starting in June 1943 until July 1943 several J1N1 Irvings from 251 Kokutai were based at Ballale Airfield. On June 17, 1943 J1N1 Irving piloted by Satoru Ono shot down PB4Y Liberator 31952. On July 7, 1943 pilot Shigetoshi Kudo shot down Hudson NZ2033 from above. Back at Rabaul, Shigetoshi Kudo was presented a ceremonial sword by Admiral Jinichi Kusaka for his nightfighter service and was officially credited with nine victories and nicknamed "King of the Night".

251 Kokutai Tail Code and Markings
251 Kokutai A6M2 / A6M3 Zeros tail code "V-???" (three digits in 100's range).
251 Kokutai / 251 Kokutai J1N2 Gekko/Irvings had tail code "V-? (one digit).

251 Kokutai Aircraft
Listing of aircraft assigned to the 251 Kokutai.

251 Kokutai Personnel (Partial List)
Shigetoshi Kudo  pilot J1N1 Gekko
Satoru Ono  pilot J1N1 Gekko
Akira Sugawara  observer J1N1 Gekko

References
Ôzora no samurai (1957) by Saburo Sakai
Samuari! (1957) by Saburo Sakai
Moonlight Interceptor (1985) details the Tainan Kokutai J1N1 Gekko / Irving operations including pilots Shigetoshi Kudo and Satoru Ono.
Naval Night Fighters by Yoji Watanabe 28-45
The Siege of Rabaul (1996) by Henry Sakaida page 38-41
Imperial Japanese Navy Aces 1937-45 (1998) by Henry Sakaida page 49-50
Thanks to Henry Sakaida, Osamu Tagaya and Edward Rogers for additional information

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