Refinement of the initial concept of Aegis system in the 1960s continued through the 1960s and 1970s, and the Mk 41 was conceived in 1976. Originally, the system was only intended to fire the RIM-66 Standard missile, but after the United States Navy decided that all VLS had to be capable of firing the Tomahawk missile, with a consequential increase in the height of the Mk 41 to accommodate the larger missile. The prototype for the launcher was tested and evaluated onboard USS Norton Sound (AVM-1). The first operational launcher was installed aboard USS Bunker Hill.