Civil War-dated ALS signed "Geo. B. McClellan," two pages on two adjoining sheets, 4.5 x 7, April 13, 1864. Letter to Colonel William Christian, in part: "Your very interesting letter of the 31st reached me some days ago, but my time has been so much occupied while in the city that I have been compelled to defer acknowledging its receipt. I am exceedingly obliged to you for it, because it presents a perfectly clear view of facts which have long been enveloped in mystery, and aids me materially in accounting for the results of that unfortunate campaign. I shall carefully peruse your letter as a very valuable historic document, which must hereafter be of service." In fine condition. Accompanied by the original mailing envelope and a full letter of authenticity from PSA/DNA. Christian fought at Bull Run and Antietam, and was later committed to the New York State Lunatic Asylum, the results of sun stroke and battle stress.