Uniform Regulations, 1864
Staff officers are to wear shoulder straps of the same description as prescribed for line officers with whom they assimilate, respectively, in rank, with the following exceptions as to centre devices:
In the medical corps, the anchor is omitted; in the paymasters' corps, an oak sprig, in silver, is substituted; in the engineer corps, a device of four oak leaves, in silver, in the form of a cross, is substituted; for professors of mathematics, the letter P, in silver relief, on plain gold circle, is substituted; for naval constructors, a live oak sprig is substituted; for chaplains, a silver cross is substituted; for secretaries, the letter S, in silver, is substituted.
Midshipmen, third assistant engineers, and clerks, are not to wear straps.
Gunners, boatswains, carpenters and sailmakers are to have shoulder straps of plain gold lace, four inches long and three- quarters of an inch wide; the boatswain to have the letter B, and the carpenter the letter C, embroidered in silver, midway upon their straps.
Source: Uniform for Officers of the United States Navy, As Prescribed in Regulations for the Uniform of the U.S. Navy, Jan. 28, 1864. Tomes, Melvain & Co., 6 Maiden Lane, New York. Entered according to Act of Congress, in the year 1864, BY TOMES, MELVAIN & CO., in the Clerk's Office of the District Court of the United States, in and for the Southern District of New-York. The text is reproduced here exactly as in the original, following the original use of capitalization and italics.