By the last week of May 1944, the largest military decision in history had been made - all of it except one word: *when.* **The Commander's Question** tells the five days at Southwick House as the record actually holds them - not the theater's lone-genius duel, but three forecast centers arguing down open telephone lines, an analogue library against the upper air, a chairman with no authority to overrule anyone, a barometer falling at a post office on the far edge of Ireland, and a supreme commander who owned the outcome in pencil, in advance, in his wallet. Underneath every weather briefing of that terrible week sat the question no instrument on Earth could answer at its own grain: *if I go, does it succeed?* The weather stood in for it - and commanders have been asking the sky's question, when they mean the outcome's question, in every go/no-go room since. Part II walks that proxy problem through a century: Kokura's clouds, the Challenger teleconference, the typhoons that were worshipped and blamed, the admiral the Navy graded twice, the photographs sent on leave with the man who read them, and the field marshal who drove home for a birthday because his side of the Channel could not see the Atlantic. Parts III and IV then do what a book in this series must: show the commander's question answered directly, on a public sealed record, under clocks that collapsed to hours - and rebuild Eisenhower's 6:30 room around the desk it never had, down to a one-page timing decision package and the single column no form can fill. Where the surviving accounts disagree, this book prints the disagreement. Eleven gallery-scale murals. Stagg read. Eisenhower decided. The whole law of the discipline is that those are two sentences.