While underwater vessels existed since the American Revolution, John Philip Holland invented the first truly practical modern submarine. His 'Holland Type VI' was the first to combine an internal combustion engine for surface travel and an electric motor for submerged operations. This dual-power system allowed the vessel to recharge its batteries while on the surface and operate stealthily underwater. The U.S. Navy purchased it in 1900 as the USS Holland. This invention fundamentally changed naval strategy, shifting focus from massive surface battleships to the threat of unseen underwater attacks. It led to the development of sonar for detection and eventually the nuclear-powered submarines that serve as a primary deterrent in modern global security.