The first attested demonstration of a fully submersible vessel was in 1638 when the Swiss chemist and engineer Mattias Crellius launched on Lake Konstanz. A ocean-facing nation may have had a use for his vessel, as it was it had long been dismissed as a curio before being burnt in its dockside berth by the Austrian army in 1647.
There was limited use of various military submarine designs during later years of the Leifian Cotton Wars of 1885-1920. Due to the problems of buoyancy, air supply and engine fumes these vessels tended to have funnels and their cannons sticking out of the water at all times, largely removing the element of surprise, however their small profile made them hard to target. True submarines at the time were powered by treadwheels, were horrendously slow and more hazardous to their crew than any enemy vessel. Even so, the Mvskokian submarine Camhcáka threatened Nanih Waiya harbour for two months in 1914, preventing the landing of Kalmar troops, before being blown out of the water.
The submarine really came of age during the Great Eastern War (1961-1967) where fully submersible vessels were first convincingly used for military purposes. They were still primitive and cumbersome and their short ranges still hampered their usefulness. However during the Battle of Yonaguni in 1965 six Chinese submarines fitted with state of the art 'torpedoes' sank three Japanese battleships.
Torpedoes were originally large explosive charges usually towed behind submarines with very wild reliability rates. More often than not nowadays they are missiles powered by clockwork and compressed air which can be launched both by surface vessels and correctly out-fitted submarines. Dropping them from airships has also been attempted, but the low flying height required makes this largely unworkable. Some submarines are fitted out with artillery guns on their decks so they can be used like conventional ships once they have surfaced.
Most countries that have a substantial offensive naval force have at least one submarine in the fleet. It is usually assumed that Kalmar has the largest and most advanced submarine fleet, followed by United Netherlands and Japan.
Offensive submarines have the issue of small operational ranges and have historically been unable to keep up with main fleets. This shortcoming is even more apparent as fleets such as the UKN's converts to oil power. However, the naval engineers of Saaremaa appear to have fixed this problem and Kalmar is now producing the most advanced, and fastest, submarines in secret docks on the islands. The secret nature of these ships is highlighted by the fact the main docks are still producing the old class of submarines to deflect attention. The new class is only known by the code name 'haí' (Estonian for shark). Newer fuel sources for torpedoes are also being tested which will increase the reliability and range of them.