Found a 2009 article from the Journal of S&W collectors on 2 inch S&W revolvers in US Military service.
It lists the Model 56 as a revolver in .38 spl., 2 inch heavy barrel, ramp front sight, US stamped on back strap, Serial #'s from K500001- K515205, and civilian possession approximately 27. In 1962 the Air Force ordered a .38 special S&W K frame revolver with adj. target sights and a 2 inch heavy barrel. S&W had not produced either its Model 14 or 15 with a 2" inch barrel at that time. The Air Force revolver had features from both and was designated by the factory as the Model 56. It was blued, had a heavy 2 inch barrel with a wide rib and plain stocks, neither the back strap nor the rear sight leaf was serrated, as is found in the Mod. 15. The Mod. 56 was marked U.S. on the back strap. A matching 5 digit assembly # stamped on left side of frame near butt, on the yoke opposite the frame and inside the side plates. Serials were not marked on the cylinder, extractor star, barrel flat or on the rear face of the yoke. MOD (over) 56 was marked on the left side of frame opposite the yoke. No P proof mark was applied. .... As of January, 2009 the Model 56 revolver, National Stock Number 1005-00-973-2058, remains in the Federal Logistics Information System as a terminal item, available for requisition by the Navy, subject to ordering until stocks are exhausted.
(Article written by K. Williams, C. Flick, & E. Archer)
It lists the Model 56 as a revolver in .38 spl., 2 inch heavy barrel, ramp front sight, US stamped on back strap, Serial #'s from K500001- K515205, and civilian possession approximately 27. In 1962 the Air Force ordered a .38 special S&W K frame revolver with adj. target sights and a 2 inch heavy barrel. S&W had not produced either its Model 14 or 15 with a 2" inch barrel at that time. The Air Force revolver had features from both and was designated by the factory as the Model 56. It was blued, had a heavy 2 inch barrel with a wide rib and plain stocks, neither the back strap nor the rear sight leaf was serrated, as is found in the Mod. 15. The Mod. 56 was marked U.S. on the back strap. A matching 5 digit assembly # stamped on left side of frame near butt, on the yoke opposite the frame and inside the side plates. Serials were not marked on the cylinder, extractor star, barrel flat or on the rear face of the yoke. MOD (over) 56 was marked on the left side of frame opposite the yoke. No P proof mark was applied. .... As of January, 2009 the Model 56 revolver, National Stock Number 1005-00-973-2058, remains in the Federal Logistics Information System as a terminal item, available for requisition by the Navy, subject to ordering until stocks are exhausted.
(Article written by K. Williams, C. Flick, & E. Archer)