Outside of his family, General William S. Rosecrans had three great passions in his life: His religion, Roman Catholicism, to which he had converted as a cadet at West Point, the Army and the Union. In the Civil War all three passions coincided. Rising to the rank of Major General and achieving command of the Army of the Cumberland, until he was removed in the aftermath of the Union defeat at Chickamauga, Rosecrans conducted himself in the field as if he were a Crusader knight of old.
Raised a Methodist, Rosecrans’ conversion was a life long turning point for him. He wrote to his family with such zeal for his new-found faith that his brother Sylvester began to take instruction in the Faith. Sylvester would convert, become a priest, and eventually be the first bishop of Columbus, Ohio.
His most precious possession was his Rosary and he said the Rosary at least once each day. In battle the Rosary would usually be in his hand as he gave commands. He had a personal chaplain, Father Patrick Treacy, who said Mass for him each morning and would busy himself the rest of the day saying masses for the troops and helping with the wounded. In battle he exposed himself to enemy fire ceaselessly as he rode behind the General. Rosecrans, after military matters were taken care of, delighted in debating theology with his staff officers late into the evening.
As a general Rosecrans was in the forefront of Union commanders until his defeat at Chickamauga. His removal from command following the battle was controversial at the time and has remained controversial, some historians seeing in it a continuation by Grant, who was placed in charge of Chattanooga following Chickamauga, of his long-standing feud with Rosecrans. Certainly Rosecrans had already drafted the plan followed by Grant to reopen the lines of supply to the Union forces in Chickamauga. Go here to read a spirited defense of General Rosecrans which appeared in issue 401 of The Catholic World in 1898.
Rosecrans resigned from the Army in 1867 and had a successful business career. He served in Congress from 1881-1885.
He narrowly missed being the first Catholic president of the United States. General James Garfield, an Ohio Republican Congressman and future president, who had served under him, telegraphed Rosecrans during the 1864 Republican Convention to see if the Democrat Rosecrans would serve as Veep on a Union ticket with Lincoln. Rosecrans gave a cautiously positive reply but Garfield never received the telegram and the nomination went to Andrew Johnson. Rosecrans suspected that the telegram had been intercepted by Rosecrans’ old nemesis, Secretary of War Stanton.
One hundred and fifty years ago Rosecrans was about to go into a battle at Stones River in Tennessee that would last from December 31, 1862-January 3, 1863. He succeeded in defeating Bragg’s Confederate Army of Tennessee and drove him from central Tennessee. It was an important victory, a needed shot in the arm for the Union after the disaster of Fredericksburg. In his hour of triumph Rosecrans knew who to thank. At the conclusion of his official report of the battle he wrote:
With all the facts of the battle fully before me, the relative numbers and positions of our troops and those of the rebels, the gallantry and obstinacy of the contest and the final result, I say, from conviction, and as public acknowledgment due to Almighty God, in closing this report, “Non nobis Domine! non nobis sed nomini tuo da gloriam.
Donald R. McClarey
Paul Zummo
Almost Chosen People 
While the general was no doubt an exemplary Catholic gentleman, Chickamauga was a disaster of the first water. Arguments and counter-arguments may fly, but the rule of Albert Sidney Johnston cuts through them all:
“The test of merit in my profession is success. It is a hard rule, but I think it is right.”
The test noted by Albert Sidney Johnston was certainly applied unevenly during the War. Burnside, for example, after the disastrous defeat at Fredericksburg, still having important commands throughout the War until after the Crater. Hooker after Chancellorsville had important commands throughout the War. Lee after Gettysburg offered his resignation but Jefferson Davis was not foolish enough to accept it. Rosecrans commanded the Department of Missouri in 1864 which was a waste of a good soldier.
A book has just come out which contends that Grant engaged in falsification in his memoirs to portray Rosecrans in the worst possible light. That seems pretty strong to me, although I am eager to read the book:
http://www.amazon.com/GENERAL-GRANT-REWRITING-HISTORY-Understanding/dp/1611211182
This seems less a case that Rosecrans should have been kept in command of the Cumberlands than a case that Burnside’s continued employment was scandalous.
I recently read a book arguing that Pap Thomas was kept down both during the war and in historical retrospect by a Grant-Sherman cabal, but the tone was so polemical and overwrought that I couldn’t give it much credence.
I think that Rosecrans was a better general than Hooker and that Chancellorsville was a worse defeat than Chickamauga. But for Jackson dying as a result of wounds at Chancellorsville, I suspect that Gettysburg might well have been a Confederate victory with Jackson conducting the attack on the first day. Hooker rendered solid service in the West following Chancellorsville and I think that the same would have been the case with Rosecrans if he had not been put on the shelf.
In regard to Thomas, Grant was about to relieve him before his smashing victory at Nashville due to his unwillingness to attack until he decided the time was right. Thomas was a Rosecrans loyalist and had to be convinced by Rosecrans to take command of the Army of the Cumberland after Rosecrans was relieved.