This is an iron-strapped, US marked frame '51 Navy in the 90XXX range. There are no sub-inspection marks or USN stampings on the butt and it doesn't appear that there ever were. There is a wonderfull plaque on the right grip that reads,"Captured by Capt. Robert Burns 4th Michigan Cavalry from a Rebel Officer at Shelbyville, Tenn. June 27, 1863". It is absolutely authentic and was inscribed close to the period of captured. Burns progressed from a Lt. to Lt. Colonel from '62 - '65. He also played an important role in capturing Jefferson Davis with the 4th. This gun comes with several pages of historic information on Burns as well as 30 or so transcribed letters written home that include one that speaks of a captured revolver. Great Stuff!