Statistics for occurrence #1 of “U. S.” in chapter 5 of Thomas Wentworth Higginson, Massachusetts in the Army and Navy during the war of 1861-1865, vol. 2:

...c. 26, 1862. First Lieutenant, Assistant Surgeon, 17th Mass. Infantry, July 3, 1863. Dismissed, Dec. 23, 1864. First Lieutenant, Assistant Surgeon, 3d Infantry, M. V. M., in service of the U. S. , Apr. 23, 1861. Mustered out, July 22, 1861. Possibly identical with Clarke, Johnson. See Massachusetts Officers in Other States. Major, Surgeon, 34th Mass. Infantry, July 3, 1862. M...
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