What makes a warship influential? Being the first of its design is certainly important, but it's not just that. Some of the most influential warships of the modern era were designed such that enemy countries actually designed new weaponry and vehicles in direct reaction to the existence of these warships. Other ships on this list aren't necessarily marvels of engineering ingenuity, but performed so beautifully that they sets a standard for others, making them tremendously influential. Then there are those ships the existence of which became the basis of a policy like a naval treaty.
This lists focuses on ships of the era post-industrial era, in which rams, oars and sail were replaced by steel, guns and steam. However, it also touches upon a few designs of the pre-industrial era, which had a major influence on future warships. Read on for a list of the most influential ships of this modern era.
The warships of the Renaissance, the galleons of the Spanish Armada, Nelson’s Victory at Trafalgar, and perhaps even today’s gun-and-missile-armed warships owe their existence to galleasses, a warship developed from merchant vessels. Technically, galleasses weren't even ships, but rather makeshift gun platforms. They contributed in part to an epochal Christian victory of the Ottoman Empire, and were responsible in part for the introduction to long-range weapons like run and cannons into naval warfare.
The all-big-guns warship concept was the brainchild of Italian designer Vittorio Cuniberti, who his concept to Allied powers when his country did not take up his idea. The Dreadnought was the first design of this nature to be completed, though two battleships were designed earlier. One was the American South Carolina. The other was the Japanese Satsuma, which got only four 12-inch guns, and was therefore more of a pre-dreadnought design in the end. Fast construction of the Dreadnought made it the first all-big-guns ship to set sail. The Dreadnought was a leader in armament and armor and propulsion systems, as it was the first capital warship to use the steam turbine of Charles Parsons.
When you talk about pioneering heavy metal, you have to include a pair of ships. These two, the Monitor and the Merrimack, fought each other in the American Civil War. Both were wooden ships fitted with iron plating, and both had unique concepts used in future designs: sloped armor on the Merrimack, and the revolving turret mounting on the Monitor. In addition, they used pure mechanical propulsion instead of wind power (ie sails).
Though not the first all-metal ship (that would be the HMS Warrior), the French Gloire was the first to practically use metal plate as armor, as well as have mechanical propulsion as a major feature. When it appeared, the Gloire made all other wooden designs obsolete in an instant. It was itself made obsolete by British Warrior, which appeared only a year later. But Gloire spurred the quantum leap in naval shipbuilding that led to the rabid design race of all-metal warships.