With so many regiments being sent east for the war effort, the 1st U.S. Cavalry was initially kept on the frontier until militia-type units were raised to protect against Indian raids. On 22 June 1861, former 1st Cavalry officer George McClellan, now a major general, requested Company A and Company E to serve as his personal escort. These two companies saw action in the Bull Run, Peninsula, Antietam and Fredericksburg campaigns, not rejoining the regiment until 1864. The rest of the 1st Cavalry was committed to action in Mississippi and Missouri.