This was an aerial night mining mission involving 32 planes from the 6th Bomb Group:
The first mission in May was flown on the night of 3-4 with thrty-three planes carrying a load of 232 aerial mines in a late afternoon takeoff to Mine Field “L” just east of the Shimonoseki Straits. The field had been mined previously and this operation was for reinforcement, i.e., replacing mines swept away or exploded. Thirty-two aircraft were effective with missions results classified as good. Enemy opposition was light, and all Sixth planes returned undamaged.
[Pirate’s Log, p. 41]
20th AF Mission 183