Today, flight numbers are often four digits. Earlier in the industry's history, lower numbers were used, and even single digits were not uncommon. Most airlines referred to them as "flights", although Braniff, for one, used the alternative term "trip". And in the piston era, it also was not unusual for at least some flights in a carrier's timetable to also carry a name.
In many ways, this reflected railroad practice of the time. Their timetables were full of expresses, locals, and specials that often reflected their destination, origin, or both. More evocative names were also used, sometimes even bordering on the fanciful. In today's marketing terminology, this was an attempt to establish branding, so that travelers would gravitate to carrier A's service rather than B's or C's.
This was true both in the U.S. (anyone recall the "Lonesome Pine Special"?) and elsewhere. The premier service between London and Paris bore the dual titling "The Golden Arrow/Fleche D'or", although 'arrow' probably wasn't the perfect term for the cross-channel boat crossing portion of the trip. Other widely recognized examples include the several versions of "Orient Express", South Africa's "Blue Train", and Germany's Rheingold.
Another railroad term that was borrowed by an airline was, appropriately, "Flyer". During the 1940s, Eastern applied this to many of its services, focusing on geography, including cities (Jacksonville, New Orleans, Chicago), regions (New England, Central American, West Indies, Everglades) and foreign points (Havana, Mexico). Even the all-cargo flight rated a name, the "Night Cargo Liner". Braniff's 'trips' of the same era included the "Texas Ranger/Texas Flyer", the "Texanaire" and "Starlite Express".
American also had a "Texan", as well as "Forty-Niner", "Southerner", "Mercury" (which became a longtime descriptor of the airline's first-class services in general) and "Statesman" on its 'Safe, Southern' U.S. transcontinental route. Interestingly, all of these were also names utilized by U.S. railroads for passenger trains. During World War II, there were also appearances by the "Plainsman", both the "President" and "Postmaster", as well as the "Night Owl" (later used by Amtrak) plus "Lone Star" and "Longhorn", evoking the state of Texas, where the carrier is now headquartered.
In the mid-1950s, Delta named a few of its DC-7 flights using terms associated with flying and speed, including "Rocket" and "Tradewind". Later, the carrier inaugurated what it termed "Royal Service" on many flights using this equipment, featuring a choice of meals and complimentary Champagne, among other amenities; the nomenclature for these flights included the "Royal Poinciana" (Chicago-Cincinnati-Atlanta-Miami); "Royal Ranger" (Chicago-St. Louis-Houston); and the somewhat more exotic "Royal Caribe", also originating in Chicago and serving New Orleans, Havana, Cuba, and Montego Bay, Jamaica prior to terminating in Caracas, Venezuela.
"Tradewind" was also used by National Airlines for its participation in southern transcontinental interchange flights between Florida and California that also involved American and Delta, in an era when no single airline had the route authority to do this. A more bizarre application was NA's use of "The Executive" for a flight that began in Miami and ended in New York...with intermediate stops in Jacksonville, Florida; Savannah, Georgia; Charleston, South Carolina; Wilmington and New Bern, in North Carolina; Richmond, Virginia; Washington, DC; and Philadelphia, Pennsylvania. For some reason, the same moniker was applied to a Jacksonville-Tampa round trip.
Airlines outside the U.S. also participated in the practice to some extent. Avianca in Colombia had "El Colombiano", "El Andino" and "El Panameno" in its timetable. Trans-Canada (Air Canada's earlier name) was another carrier that had a named all-cargo service, the "Flying Merchant". Competitor Canadian Pacific, limited to a single daily east-west trip across Canada in the late 1950s called its entry the "Canadian Empress", another cross-modal reference, since the company's ships all carried the "Empress" name, as well.
As of 1959, Air France's premier New York-Paris service was the all-deluxe class Lockheed 1649 Starliner that operated once weekly in each direction, dubbed the "Parisien Special" and "Golden Parisien". Service to Tokyo included the "Champs Elysées" and the "Dragon Vert" (Hong Kong was an intermediate point), while the flight ending in Mauritius was the "Étoile des Isles". A single trip in the Paris-London schedule, the 1200 Noon departure in both directions, was dubbed the "Epicurean", perhaps as a subtle reminder to potential UK customers about what the carrier likely believed was its superior cuisine.
BOAC, Britain's long-haul carrier of that era, promoted its prime New York-London service as the "Monarch", which certainly avoided the need to change when there was a gender shift in the office. This term survived into the jet age, being used on the first transatlantic jet service with the Comet 4, and later was expanded to cover all JFK-LHR service during the 1960s, with care being taken to add the word "Scottish" as a prefix to the trip that stopped at Glasgow's Prestwick Airport prior to terminating at Manchester.
Alas, in more modern times, this practice has fallen into what the British term "disuse", likely for a number of reasons, including the plethora of services (flights, trips, etc.) provided by today's air transport system, and the fact that aircraft are now used very interchangeably on many routes. Some would argue that the concept of a distinctive service is no longer widely present, either. Besides, as the industry consolidates, it's going to be difficult enough to contend with five-digit flight numbers...