The US Navy has always been interested in testing new propulsion technologies or combining what's already on-the-shelf in new ways for greater efficiency. The new Zumwalt class destroyers, for example, will have gas turbine-electric propulsion provided by two Rolls Royce Trent jet engines. While the turbine-electric propulsion setup and the make of engine are new to the US Navy, jet engines have been stuck into ships for decades - and for just as long, the Navy has stuck with one specific jet engine in particular. The Trents in Zumwalt potentially signals the end of the Navy's near single-source gas turbine acquisition policy as aerospace manufacturers play a neverending game of one-upmanship.
Anybody who's ever worked on a large twin-jet can probably recognize the specific object above. It's a General Electric LM2500 gas turbine, which shares the same "core" as the CF6 high-bypass engine slung underneath a very large percentage of the world's widebody aircraft as well as the Boeing 757. Here it's powering the Oliver Hazard Perry class missile frigate USS Ford during the Desert Storm timeframe. The Perry class, or alternatively the FFG-7 or "OHP" class is the most numerous class of escort vessel ever commissioned by the US Navy with a few foreign navies operating them as well (some buying used ships, some ordering them new or building licensed copies themselves). Each and every one is powered by a pair of LM2500s. In fact the LM2500 specifically powers nearly every non-nuclear vessel in the fleet - the entire run of DDG-51 Arleigh Burke missile destroyers and CG-47 Ticonderoga missile cruisers, the Suppy class of, well, supply ships, the amphibious assault ship (think mini-carrier that can land troops) USS Makin Island (the first such type of vessel in US Navy service to be powered by gas turbines) the Independence class of Littoral Combat Ship and the now-retired Spruance class sub-hunting destroyer, the first mass application of the LM2500 in US Navy service.
Each gas turbine is self-contained in a modular structure as seen above, being lowered into the hull of USS Bunker Hill, a CG-47 class cruiser. Bunker Hill has two other units for a total of four, like most large US Navy vessels. This has pretty much been the way it has been. Other manufacturers have other gas turbines available - but the LM2500's proven service in large yet fast vessels has made it a known quantity and a major selling point. In fact, LM2500 engines can be found all over the world in the destroyers and aircraft carriers of Italy, Japan, Korea, Spain, Germany and others.
The Rolls Royce MT30, the ship-packaged version of the Trent aero-engine, seems to be gaining serious traction as a major LM2500-fighter. In addition to Zumwalt two are fitted into the Freedom class Littoral Combat Ships, competing against the LM2500-powered Independence class vessels. They also power the Queen Elizabeth class aircraft carriers, the first of which has just been christened. Perhaps most impressive is how small of a ship they can squeeze into, including the Republic of Korean Navy Incheon class frigate. Roughly the same size as an LCS, these frigates area also meant for operating in a "green water" environment close to shore and far from the open ocean, but are more honed towards the unique requirement of battling the North Korean navy including being equipped with a heavier 5-inch gun usually found on destroyers and cruisers.
Rolls Royce established a proud tradition of marine gas turbines early, including the very first to power a commissioned warship (a small Finnish vessel) and the first in a large commissioned warship in HMS Exmouth all the way back in the 50s. "Large" is a relative term in naval weaponry however, and although RR has much success in powering 5,000 ton frigates all over the globe, they've largely missed the boat on 9,000-10,000 ton and larger vessels that overwhelmingly prefer LM2500 power. The MT30 might be a game changer for them, however, and just as the Trent is displacing the CF6 from the commercial aviation throne, the MT30 seems poised to give the LM2500 serious competition.