Thumpalumpacus
Major
The battle off Bougainville (Feb 20 1942) is a particularly interesting one, in terms of looking at USN 5in AA performance. USN CAP reported the 5in AA fire from the USN TF was almost completely ineffective, and Lundstrom notes only two IJN bombers were damaged and/or downed by close range AA but only after the bombers had been damaged by CAP, yet the USN awarded 6 confirmed AA kills. The USN CAP made 15 kill claims and SBDs several more, so against 17 bombers the USN awarded 6 AA kills, despite ~17 CAP kill claims!
Yeah, USN AA was pretty miserable at that point in the war, two-and-a-half months into our American involvement. I think that's pretty understandable given the state of technology at the time.