The Conference established the nautical date line and adopted an ideal form of the terrestrial time zone system for use at sea.
This recommendation was adopted between 1920 and 1925 by all major fleets, including British, French and American.
Nevertheless, up to the Second World War, the old practice of keeping local apparent time prevailed on many independent merchant ships.
The nautical date line is implied but not explicitly drawn on time zone maps.
It follows the 180° meridian except where it is interrupted by territorial waters adjacent to land, forming gaps: it is a pole-to-pole dashed line.