The U.S. Navy is fitting new Rolls Royce water jets to its Littoral Combat Ships (LCS). Originally designed for a cancelled ship program, four of the new Axial-Flow Waterjet Mk-1 engines will be fitted over the next two years to the U.S. Navy’s fifth LCS, USS Milwaukee (LCS-5) at the Marinette Marine shipyard in Wisconsin, with ten of the class to follow.

The new water jets replace earlier commercial jet systems and, according to the Navy, can pump out half a million gallons (1.9 million liters) of high-density seawater per minute, pushing the LCS at over 40 knots (46 mph, 74 km/h) while providing more power for less weight.

The engines were developed by Rolls-Royce Naval Marine in collaboration with the Office of Naval Research (ONR) and the Naval Surface Warfare Center, Carderock Division, and their purpose is to increase the speed of the LCS while lowering running costs. They do this in part by reducing cavitation, which is what happens when a poorly engineered propeller or turbine runs at high speed and generates bubbles. When these bubbles collapse, they produce spots of high temperature and shock waves that can severely damage equipment.

The LCS are a new class of warships designed to help the Navy deal with post-Cold War naval requirements. They come in two variants, a conventional hull and a trimaran, and are similar to corvettes, though with assault ship capabilities such as a landing deck, a hanger large enough for two SH-60 Sea Hawk helicopters and the ability to launch a small armored assault force. They’re meant to be small, inexpensive and modular with flexible mission capabilities with an emphasis on operating in shallow coastal waters. Much of the design can be swapped out depending on the mission, as too can assets which can be launched from the LCS by smaller vessels, aircraft and unmanned vehicles, which keeps the ship itself out of harm’s way.

A Navy press release said that the Mk-1 will reduce maintenance costs and increase the engine system’s lifespan, though some critics have said that the new jets will be extremely noisy and make it difficult to the LCS to carry out littoral anti-submarine operations.

Source: US Navy