This was called the Cal .45 revolver ball Cartridge Model of 1909 for Single and Double Action revolvers. It was developed from an earlier modified Colt round in order to standardise a cartridge able to function in both the newly manufactured double action revolver and existing single action revolvers still in action in the Philippines. The Model 1909 was to replace various .38-cal. revolvers that repeatedly struggled to stop fanatical attackers in the then-ongoing Philippine Insurrection. It is a well-established part of shooting lore that the U.S. military went back to the .45 Colt after dissatisfaction with the stopping power of its .38 revolvers in the early 1900s and  although a superb heavy-duty handgun, was fielded in relatively small numbers and had the shortest service life of any issue sidearm in our nation’s history. The adoption of the iconic Colt M1911—and its storied service in conflicts arising shortly after its fielding—largely drown out the stopgap service of the M1909. (Erlmeier, Brandt Ref. 432).