According to Wikipedia: "The Mark 46 torpedo is the backbone of the United States Navy's lightweight anti-submarine warfare torpedo inventory, and is the current NATO standard. These aerial torpedoes are designed to attack high-performance submarines, and current variants, such as the Mark 46 Mod 5, are expected to remain in service until the year 2015. In 1989, a major upgrade program for the Mod 5 began to improve its shallow-water performance, resulting in the Mod 5A and Mod 5A(S)."