American side of Rabaul Mission January 5, 1943
Research by Justin Taylan

January 5, 1943 Mission 4L: six B-17s and six B-24s took off from 7-Mile Drome near Port Moresby to bomb Rabaul, shipping Simpson Harbor and the airfield at Rabaul. The American formations arrived over Rabaul in three groups, at different local times:

0925
2 B-17s bomb Vunakanau dispersal area, and are intercepted by by 12-15 ZEKES.
They claim 7.
 
1200
6 B-24s attach ships in Rabaul's Harbor, they are intercepted by 12-15 fighters mostly ZEKES but possible "Me 109s" (Mis-identified Ki-43 Oscars). They claim 2.
 
1200-1210
6 B-17s. Rabaul ships. Intercepted by 8-10 ZEKES and possible HAPS. No claims.
[ General Walker's B-17F "San Antonio Rose" 41-24458 was part of this last group. ]

American Losses
Two B-17s were lost, B-17F 41-24538 and B-17F "San Antonio Rose" 41-24458 with Brigadier General Kenneth Walker, Commanding General V Bomber Command aboard.

Misidentifcation of Me-109
Both old and new type Zero noted as well as E/A resembling ME109. Enemy aircraft made determined attacks mostly from the front quarter". The 'ME-109s' were likely Ki-43 of the 11th Sentai.

In the South Pacific, there were many reports of 'Me-109s', often when pilots confused the Ki-61 Tony for that aircraft.  In this case, the aircraft were not Ki-61s as the first unit with this type (68th Sentai) did not arrive at Rabaul until April 1943, three months later.

Japanese side of Rabaul Mission January 5, 1943
Research by Richard Dunn

Both the Japanese Navy (Zeros) and Army (Oscars) intercepted this raid. The army and navy shared Rabaul air defence. The navy took the early shift and intercepted the first raid. The army apparently took the later shift and took on the B-17/B-24 formation. The evidence points to the fact that Walker's B-17 was shot down by a Ki-43-I Oscar. The fact that there was some recognition descrepencies in the raid may be additional evidence that Ki-43 Oscars (less familiar aircraft) were involved, and mistaken as HAPS or Me-109s.

Japanese Navy Interception
Japanese Mono. # 121 (Navy) says 3 B-17s raided Rabaul. 12 fighters intercepted (A6M Zeros of the 582nd Kōkūtai). They claim 1 B-17 shot down.  [ the 0925 raid]
 
Japanese Army Air Force Interception
Japanese Mono. # 37 (Army) says two air attacks by about 5 B-17s and B-24s (5 each?). Part of the 11th Sentai (Ki-43-I Oscars) intercepted and claimed 4 (including 3 doubtful). A translated Japanese Army Intelligence is more specific about claims saying 2 B-17s (1 probable) and 2 Consolidated (probables) were shot down. Three Japanese aircraft were lost but all pilots were saved. The second B-17 limped close to Goodenough before ditching (403 BS). [this suggests that B-17F 41-24538 was claimed as the probable and Walker's B-17F "San Antonio Rose" 41-24458 was the certain victory which might mean it was seen to crash] 

Anti-Aircraft Fire
Significant, is that there is no report of damage to US a/c by AA guns. However, heavy anti-aircraft guns were in action.

50th AA Battalion
Located at East Airdrome [Lakunai Airfield]. 0730 air-raid alarm, 2 B-17s, coming from south, alt. 5000m, out of range, couldn't fire. Notice Japanese times are all 2 hours earlier than Allied "L" time zone times.
 
1030 - OP sighted 12 a/c, 5 B-17, 7 B-24, from 2700 direction, No. 1 & 2 secs opened fire, alt 3000m, enemy a/c broke formation while dropping bombs. No. 3 sec opened fire on rear section of bombers, alt. 3500m. Nothing hit, enemy pursued by our fighters and disappeared to the south. There is a sketch that shows no approach route but two withdrawal routes both starting from NE Simpson Harbor (my estimate, no location names included) one on about a 170 deg. track and the other about 135 deg. [their guns appear to be in range of this track]. Report continues. "No crash." They suffered three wounded from straffing and bomb fragments. They only expended 8 rounds.
 
15th Machine Cannon Battery
[Rabaul Harbor] Air raid warning 0730. At 0735 2 B-17Es came in toward rabaul from the north (alt. approx. 5000m) "but because of our A/A fire they fled to SW. Note "our A/A fire" probably relates not to the battery's machine cannon (captured US .50's) but to heavy AA guns. Since the 50th apparently only fired 8 rounds, this was probably mostly from the 39th.
 
1010 formation of 8 B-17s approached rabaul from NE (alt. approx 3500m) and dropped several bombs in the harbor. No damage was sustained and because of our A/A fire, they suddenly changed course and fled to SW. Battery did not open fire as the airplanes were out of range.

39th AA Battalion
(Don't have ops orders or a war diary for them).

15th Battalion
Had a false alarm but no raid on 6th. I didn't copy that page for the 15th so I suspect there was nothing of interest on that day.