The United Nations Naval Service is a futuristic fictional military organisation created by David Feintuch in his Seafort Saga series of novels. The organisation is heavily based on the Napoleonic-era Royal Navy, including the presence of teenage officers serving aboard major ships, largely illiterate lower-deck crewmembers, and draconian discipline. The command structure is extremely simplified compared with modern military organisations, with 'line' officers proceeding from Cadet to Midshipman (often abbreviated to 'Middy'), Lieutenant (the lowest commissioned rank), Commander, Captain, Admiral, and Fleet Admiral. The UNNS operates FTL interstellar vessels on multi-year voyages between Earth and several colonies. The series follows the career of a UNNS officer, Nicholas Seafort.
The series takes place in the years just preceding and decades after 2200. A reformed UN has become the world government, as well as administrating Earth's colonies. Other political organizations, such as the US presidency, have only regional authority. The Secretary General is similar to a President of Earth.
Keeping with the Napoleonic-era theme, the world has become very religious, and in some cases social customs have reverted. For example, swearing in public can lead to legal difficulty, duels are legal, and the Unified Christian Church holds much sway over the public.
Technological advancements include the discovery of N-waves, which are used to travel faster than the speed of light, advanced and sentient AI, and weaponized lasers.