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April 2011 www.sname.org/sname/mt Waterjet HE LAST DECADE has seen steadily growing interest in small, high- speed combatant craft and ships. Vessels with shallow draft and the capability for high speed are used in a range of lengths and displace- ments for patrol vessels. Many of these vessels are powered by waterjet propul- sion, which provides high propulsive e ciency at high speeds, shallow draft, and vectorable thrust at low ship speed. ese qualities are well suited to vessels that operate in the littoral zone, must be highly maneuverable, and require acceleration capability and sustained speed to e ectively prosecute missions. Recently, there has been growth in both the size and the power lev- els of waterjet propulsion systems being employed on these combat- ant craft. Perhaps the most notable example is the United States Navys littoral combat ship (LCS) program, where shallow-draft vessels weighing approximately 3,000 tons are powered by large waterjet propulsion systems to reach speeds in excess of 40 knots. A propulsion system with high power density is essential to many small combatant applications. High power density propulsion minimizes the footprint of the propulsion system on the vessel design with respect to both Exploring high power density waterjet propulsion for small combatants THE MODEL BY FRANK LANNI Rolls-Royces new compact high power density Axial Mk1 waterjet currently under construction for the O ce of Naval Research and the littoral combat ship program.