On the outbreak of the Civil War, Halleck put aside his entrepreneurial ventures to return to service as a major-general. In November 1861, he was put in charge of the Department of Missouri. The success of his forces under Ulysses S. Grant at Fort Henry and Donelson, his command was enlarged to include the Department of Mississippi. His enlarged command won victories at Pea Ridge, Island #10, and Shiloh. Taking immediate command of his three united field armies after the latter Battle, at Corinth, he proved to be an incapable field commander in his only campaign. Since he failed as a field commander, he was brought to Washington as general in chief until Grant's promotion in March 1864 resulted in Halleck being demoted to chief of staff, but with many of the same duties since Grant served on field command in the last campaigns of the Eastern theater.
