The conference recommended that the standard apply to all ships, both military and civilian. The establishment of nautical standard times, nautical standard time zones and the nautical date line were recommended by the Anglo-French Conference on Time-keeping at Sea in 1917. Prior to 1920, ships kept solar time on the high seas by setting their clocks at night or at the morning sight so that, given the ship's speed and direction, it would be 12 o'clock when the sun crossed the ship's meridian. It is typically only used for trans-oceanic travel, as captains will often not change the timekeeping for short distances such as channels or inland seas. This time-keeping method is only used for radio communications and to account for slight inaccuracies that using Greenwich Mean Time (GMT) may lead to during navigation of the high seas. Nautical time keeping dates back to the early 20th century as a standard way to keep time at sea, although it largely only applied to military fleets pre–World War 2. Nautical time divides the globe into 24 nautical time zones with hourly clock offsets, spaced at 15 degrees by longitudinal coordinate, with no political deviation.

Nautical time is a maritime time standard established in the 1920s to allow ships on high seas to coordinate their local time with other ships, consistent with a long nautical tradition of accurate celestial navigation. System that allows ships on sea to express their local time

Define gmt time zone