A good article on General Rosecrans:
William Starke Rosecrans (1819-1898) would become one of the most famous generals of the Civil War. He also was a single-minded and zealous booster of the Catholic faith.
Rosecrans’s father, Crandall Rosecrans, a veteran of the War of 1812 and a descendant of Dutch-Scandinavian immigrants to the New World, baptized William in the Episcopal faith. He studied and graduated from West Point, a bastion of American Protestantism, where he subsequently taught engineering. He was, in other words, an unlikely candidate to become one of the most important nineteenth-century American converts to Catholicism.
It was while teaching at West Point in the 1840s that Rosecrans converted to Catholicism. One of his daughters, Anita, later claimed he bought a book on Catholicism because he figured that if he was going to take the time to learn about various religious traditions, he might as well add Catholicism to the mix. After an intense period of study, he was conditionally baptized a Catholic in 1844, because of a lack of confidence in the validity of his Episcopal baptism.
Go here to read the rest. His Tullahoma campaign, which almost bloodlessly conquered central Tennessee, was one of the true strategic masterpieces of the Civil War.
Rosecrans was made to lead the future drive on Atlanta, but misfortune at Chickamauga, and the unending enmity of Grant, made that a might have been.


The priest was Fr Jeremiah Trecy. Not Patrick.
Jeremiah did offer masses and sacraments at different times for both the Blue and the Gray. He also served later in northeast Nebraska (Jackson) and in South Dakota.
https://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/trecy-jeremiah
Mentions his association in the civil war