International Meridian Conference
On 11 October 1883, a convention of railroad executives met in Chicago and agreed to the implementation of five time zones in North America, using as a basis Greenwich Mean Time. Before the invitations to the Washington conference were sent out on December 1, the joint efforts of Abbe, Fleming and William Frederick Allen, Secretary of the US railways' "General Time Convention" and Managing Editor of the "Travellers' Official Guide to the Railways", had brought the US railway companies to an agreement which led to standard railway time being introduced at noon on 18 November 1883 across the nation. Although this was not legally established until 1918, there was thus a strong sense of "fait accompli" that preceded the Washington conference, although setting local times was not part of the remit of the conference.
Coordinated Universal Time
The time zone using UTC is sometimes denoted or by the letter "Z"—a reference to the equivalent nautical time zone (GMT), which has been denoted by a "Z" since about 1950. Time zones were identified by successive letters of the alphabet and the Greenwich time zone was marked by a "Z" as it was the point of origin. The letter also refers to the "zone description" of zero hours, which has been used since 1920 (see time zone history). Since the NATO phonetic alphabet word for "Z" is "Zulu", UTC is sometimes known as "Zulu time". This is especially true in aviation, where "Zulu" is the universal standard. This ensures that all pilots, regardless of location, are using the same 24-hour clock, thus avoiding confusion when flying between time zones. See the list of military time zones for letters used in addition to "Z" in qualifying time zones other than Greenwich.