All U.S. submarines were numbered in a single series with the exception of six specialized craft until the advent of the Seawolf, which is designated SSN 21 to indicate the 21st century. The Seawolf is the U.S. Navy's third submarine of that name. The first was SS 197, the second SSN 575, the Navy's second nuclear-propelled submarine which was decommissioned on July 10, 1987. She is the US Navy's latest submarine, and can dive faster, deeper and has more weapon systems than previous class boats. The new propeller design and stealth technology make this boat the most advanced in the world.