Complex sentence: The corps was initially commanded by O.M. Mitchell, who died in October 1862; he was succeeded by John M. Brannin, David Hunter, and Quincy A. Gillmore.
Split into simpler sentences: The corps was initially commanded by Ormsby M. Mitchel, who died in October 1862. He was succeeded by John M. Brannin, David Hunter, and Quincy A. Gillmore.