Today (well, it’s still October 13 where I am, anyway) is when Henry V’s campaign in France started to turn south for the English. I mean, literally, turned south (or like, southeast-ish).
What happened was, the English had conquered Harfleur and were heading back to Calais. They were in pretty good shape—there was a bit of lingering dysentery, but it wasn’t too bad, and the food supplies were sufficient. They just had to cross the Somme River and head up north. Everything was looking good until today, when the advance guard caught a random Frenchman, who told them that there was a French force of several thousand waiting across the Somme where the English had planned to cross it. This forced the English to turn away from Calais and march along the river hoping to find a suitable place to cross while trying to evade the French, their supplies dwindling all the way.