In 1887 a new concealed hammer design for police was made. Variations of this design are still being made. In 1899, S&W brought out its most famous design, the Military & Police pistol. It was a double-action which set a standard for modern revolvers. It also introduced what has become a very popular caliber, the .38 S&W Special. It is still one of the most popular revolver cartridges ever produced. Large numbers of S&W .38 special handguns were sold to police and military worldwide. They were used in both World War I and World War II. They remained popular until they were finally replaced by many police and military organizations by Semi-automatic pistols.