I asked something similar in NichtLebenZeitToeten's thread about the lack of American war cries in WWII, and it was suggested that I make a new post for this question.
The rebel yell was used to intimidate union soldiers during the American Civil War. But did its popularity die out with that conflict?
I've seen several pictures of US soldiers from World War II with or in front of confederate flags (for example, here--did soldiers also go into battle using the rebel yell?
Also, can anyone shed any insight onto pro-confederacy soldiers fighting in wars like the Spanish-American War, WWI, and WWII--were there any? Were they fighting with the union in mind, or in the spirit of the confederacy?
As far as veterans of the civil war fighting in subsequent wars, the Spanish-American war was seen by both north and south as a "great healing" between the two. President Mckinley's administration went out of it's way to appoint ex-confederate generals to leadership positions in order to bind up old wounds.
Notably, Gen. Joseph Wheeler from Alabama fought for the Confederacy and was at the battle of Shiloh. During the Spanish-American war, he volunteered and was placed in command of the cavalry division sent to Cuba. This put him in charge of Teddy Roosevelt's Rough Rider outfit.
As far as WW1, the youngest soldiers from the civil war would have been in their mid-to-late 50s at the beginning of America's entrance to that fight. John Clem was the last civil war veteran to retire from the US army and he did so in 1915