4th Kōkūtai (4th Air Group)
Imperial Japanese Navy (IJN)

Background
The 4th Kōkūtai (4th Kokutai, 4th Ku) was a land based unit of the Imperial Japanese Navy (IJN). In English, 4th Air Group. The group operated was established at Rabaul and had a fighter butai operating the Type 96 (A5M4 Claude) and later A6M2 Model 21 Zero from Lakunai Airfield and a bomber butai operating the Type 1 Attack Bomber (G4M Betty) from Vunakanau Airfield. On November 1, 1942 the bomber butai was redesignated 703 Kōkūtai (703 Air Group).

Wartime History
On February 10, 1942 the 4th Kōkūtai was established at Rabaul. To form the cadre of the group, one chutai from the Chitose Kokutai was transfered to the newly established group. The fighter butai was equipped with the Type 96 (A5M4 Claude) and later the A6M2 Model 21 Zero at Lakunai Airfield. The bomber butai operating the Type 1 Attack Bomber (G4M1 Betty) at Vunakanau Airfield.

On February 17, 1942 six A6M2 Zero took off from Shoho and land at Lakunai Airfield where they are assigned to the 4th Kokutai and become the first Zeros based at Rabaul.

On February 20, 1942 Japanese spots U.S. Navy (USN) Task Force 11 (TF-11) and at approximately 11:20am G4M1 Bettys from the 4th Ku took off from Vunakanau Airfield armed with bombs to intercept. At 1:35pm the 2nd Chutai spotted the enemy and began the attack. At 2:00pm the 1st Chutai spotted the enemy and attacked. Damaged by F4F Wildcat piloted by Lt. Edward "Butch" O'Hare from VF-3 and shot down by anti-aircraft fire was G4M1 Betty F-348 commander Lt. Commander Takuzo Ito (KIA). Damaged was G4M1 Betty pilot Ito that ditched in N. Lagoon.

On February 23, 1942 in the morning, six Zeros scrambled to intercept the first U.S. bombing mission against Rabaul when a formation of B-17 Flying Fortresses bombed shipping in Simpson Harbor. The intercepting Zeros fired at the bombers and claimed a victory. In fact, any damage inflicted was superficial. Some gunfire hit did hit the tail of B-17E Flying Fortress 41-2446 (aka "Swamp Ghost") later force landed due to low fuel.

On February 24, 1942 A6M2 Zero pilot F1/C Kokubun intercepts a B-17 Flying Fortress over Gasmata.

On February 28, 1942 six Zeros took off from Lakunai Airfield on a mission to escort G4M1 Bettys from Vunakanau Airfield on a bombing mission against Port Moresby. Over the target, the Zeros met no resistance so they tested their guns on the wreck of the SS Pruth, then strafed strafed flying boats moored in Fairfax Harbor off Napa Napa and sink Catalina A24-3 and Catalina A24-6. During the attack, A6M2 Zero 911 piloted by Sea1c Katsuro Nagatomo was hit by gunfire from a single 7.7mm Lewis machine gun and crashed into Bootless Bay.

During early March 1942 the 4th Kokutai moved to Lae Airfield at Lae.

On March 14, 1942 at 7:10am eight G4M1 Bettys took off from Lae Airfield escorted by twelve A6M2 Zeros on a strike against Horn Island Airfield. Arriving over Horn Island at 11:25am, they dropped 78 x 60kg bombs while the Zeros strafed the airfield area. Thirty-two bombs hit the western portion of Horn Island Airfield destroyed Hudson A16-136 and damaging Hudson A16-102 along with a fuel dump and some damage to the RAAF bivouac area. No one was killed on the ground. Intercepted by P-40s of the 49th Fighter Group, 7th Fighter Squadron that shot down two Zeros and claimed one bomber. During the air combat, P-40E pilot Sanford was lost. Lost is A6M2 Zero 4443 pilot Lt(jg) Nobuhiro Iwasaki (KIA) and A6M2 pilot Oishi (KIA) was deliberately rammed by P-40E "Poopy" piloted by 2nd Lt. A. T. House whose guns were jammed and although damaged by managed to land safely.

On March 18, 1942 between 9:30am to 10:00am twenty A6M2 Zeros lead by three G4M1 Bettys took off from Lae Airfield on a reconnaissance and strike against Horn Island Airfield. Arriving at 1:00pm, they find no Allied fighters. On the return flight, they strafe MV Canberra firing 700 rounds at it and wounding 13 aboard. Afterwards, all attacking aircraft return to Lae Airfield by 2:40pm.

On March 23, 1942 three A6M2 Zeros took off from Lae Airfield then rendezvous over Lae to escort nineteen G3M1 Nells from the 1st Kokutai that took off from Vunakanau Airfield near Rabaul on a bombing mission against Port Moresby. Facing no enemy aircraft, the escorting Zeros dove down to strafe 7-Mile Drome. Damaged by anti-aircraft fire is A6M2 Zero pilot Yoshi'i (KIA).

On November 1, 1942 the Imperial Japanese Navy (IJN) renamed air groups with three digit identifiers and the 4th Kokutai "Ohashi Butai" named for Commanding Officer (C.O.) Captain Fujiro Ohashi operating from Vunakanau Airfield near Rabaul was redesignated 703 Kōkūtai (703 Air Group). Aircraft tail code "S-"

Tail Codes
F-151–F-169  used at Rabaul February 1942–March 1942

References
Kodochosho, 4th Kōkūtai, February 23, 1942
War Diary 1942 (1984)
Combined Fleet - IJN Shoho: Tabular Record of Movement

Contribute Information
Do you have photos or additional information to add?