Command Of The Sea

A naval force has command of the sea when it is so strong that its rivals cannot attack it directly. Also called sea control, this dominance may apply to its surrounding waters (i.e., the littoral) or may extend far into the oceans, meaning the country has a blue-water navy. It is the naval equivalent of air superiority.

With command of the sea, a country (or alliance) can ensure that its own military and merchant ships can move around at will, while its rivals are forced either to stay in port or to try to evade it. Most famously, the British Royal Navy held command of the sea for long periods from the 18th to the early 20th century, allowing Britain and its allies to trade and to move troops and supplies easily in wartime while its enemies could not (the importance of which is reflected in the famous British patriotic song, "Rule, Britannia!," which contains the exhotation, "Rule Britannia! Britannia rule the waves", even if this was not the poem's original subject). For example, Britain was able to blockade France during the Napoleonic Wars, the United States during the War of 1812, and Germany during World War I.
Few navies can operate as blue-water navies, but "many States are converting green-water navies to blue-water navies and this will increase military use of foreign Exclusive Economic Zones [littoral zone to 200 nautical miles (370 km)] with possible repercussions for the EEZ regime.