Lee was not alone
Hundreds of officers in the U.S. Army, Navy, and Marine Corps–including Robert E. Lee-resigned their commissions when their home or adopted states seceded. The officers' letters were addressed to their commanders, the adjutant general, the secretary of war or navy, or even the President. Sometimes these resignations followed the acceptance of commissions in the Confederate States Army or state armies.
National Archives, Records of the Adjutant General's Office, 1780's – 1917
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