(Apologies for the huge thread drift, but the thread title is "On this Day".)
... and on this day in 1941, (to almost audible sighs of relief all round in beleagured Blighty), Herr Hitler made what was quite possibly his biggest mistake in WW2 in launching Operation Barbarossa. Six weeks late thanks to the Balkan/Greek sideshow forced upon him by the Allied... (call it what you will) into Greece.
Greece was a disaster for the Allies, but when viewed long term, it may well have been (an unwitting) war winnner. Put into chess terms, it was a bit like sacrificing your Queen early in the game, but because of that move, going on to win the game.
Quite a few historians have suggested that had the Germans invaded Russia six weeks earlier, as was their original plan, they would almost certainly have captured Moscow before the winter, and a book only recently released on the (until now largely ignored) 1941 Battle of Moscow makes it plain that had Moscow fallen, Stalin, and therefore Russia would almost certainly have collapsed.
...and quite probably, none of us would be here discussing anything even vaguely military - at least not in English.