Redoubt 9 was held by approximately 130 British regulars and German auxiliaries. Around 400 French soldiers assaulted the redoubt under the cover of darkness, taking it while suffering twenty-five percent casualties.
The fighting was hand-to-hand and savage. French troops committed fratricide when they mistook their own German troops, the Royal Deux-Ponts, with those of the enemy – who also wore blue coats. “Anyone can imagine what happened once we were inside the redoubt,” recalled Private Georg Daniel Flohr of the Royal Deux-Ponts after the battle. “People of four nations were thrown together: Frenchmen, English, Scots, and Germans . . . the soldiers . . . were so furious that our people were killing one another . . . The French were striking down everyone in a blue coat. Since the Deux-Ponts wore blue, many of us were stabbed to death . . . One screamed here, the other there, that for the grace of God we should kill him off completely. The whole redoubt was so full of dead and wounded that one had to walk on top of them.”
https://allthingsliberty.com/2020/04/what-they-saw-and-did-at-yorktowns-redoubts-9-and-10/
National Museum of American History