(1) Initiate search in the Bismarck sea.
(2) USN search=1 & IJN search=2, which gives the US 4 SPs.
(3) Elect to fight a surface.
(4) Use all four surprise points to increase IJN risk from X, D, 2A to 2X.
(5) Sink the CVL Chiyoda.
(6) MWiF then doesn't even attempt to apply the USN risk (A).
My poor tactical decision was using the 4 SPs to increase IJN risk. The X, D was sufficient to ensure the sinking of the CVL Chiyoda. That is, even if it passed the X risk (i.e., is damaged instead of being sunk) it's defense factor would increase by 1 to 10 which ensures that D will sink it. Tactically I should have used the SPs to reduce the USN risk from A to none.
