When would the Aichi D3A Val and Nakajima B5N Kate have been relegated to second-line duties?
Short answerThe panel places the transition around 1944-1945, when their intended successors were approaching service.
NotesThe answer dates the likely transition to roughly 1944 or 1945. Its reasoning is replacement-driven: that is when successor aircraft were about to enter service. The exchange provides a simple chronology for understanding how Japanese carrier aviation expected to refresh its strike aircraft. It also helps separate an aircraft becoming second-line from its immediate disappearance from all operational use.