Question:
Losses to Naval Units: Are these allocated after each air attack, or after all air attacks in a player turn?
Answer:
Rule 20G2g defines how this happens for both 20G2g & h: “For each air operation, resolve all bombing attacks of air units flying this mission before applying any hits achieved. (Keep track of the total number of hits achieved.) Apply the hits after all air units on this mission [naval units in port bombing] have finished bombing.” This means you do it on a per-air-operation basis, applying all hits (losses) to the naval units once all bombing attacks in the operation are over.
Source:
Errata published at http://www.hmsgrd.com/Files/Europa/Second Front/Second Front.pdf
