A supersonic missile is technically any missile that travels faster than Mach 1, as a number of cruise missiles do. However, sometimes the term is specifically used to refer to the next-generation, faster missiles with speeds of Mach 2 to Mach 3. These missiles, which include the Indian-Russian BrahMos, the Russian Moskit (Mosquito), and the American Coyote, are popular for anti-ship warfare plans, because their great speed would only allow a theoretical response time of 20-30 seconds, as opposed to the 120-150 second response time permitted by subsonic missiles like the American Tomahawk or French Exocet. Supersonic missiles use ramjet engines, 4X for the Moskit and Coyote and 2X for the BrahMos.
Using ramjets for propulsion, these supersonic missiles are also known as air-breathing missiles. Ramjets use rapidly inflowing air to oxidize rocket fuel, obviating the need for an on-board oxidizer, allowing a greater weight-payload ratio and increasing top speed. They also lack moving parts, making them more straightforward to mass produce and convenient for supersonic missile applications.
Supersonic missiles tend to be 2-3 times heavier than their subsonic counterparts, in the neighborhood of three tons rather than just one. According to a NATO analysis, Russian Moskit missiles are among the greatest possible threats to friendly navies, being used by the armies of Russia, China, and probably Iran. Directed energy and laser-based systems are being developed to shoot down these supersonic missiles before they can hit friendly ships.
Many supersonic missiles are sea skimmers, traveling about 20 m (66 ft) over the water for the 50 - 300 km (31 - 186 miles) to their target. The Moskit, being slightly older, has a range of 120 km (75 miles) and the BrahMos and Coyote (newer) have a range of 300 km (186 miles). Supersonic missiles can be nuclear-tipped, which would be devastating to enemy navies if deployed successfully. The existence of these missiles makes one question the effectiveness of the capital ship paradigm in modern navies.