An Accurate Timepiece for the Air Navigation age

Whilst Santos-Dumont had flown with his famous Cartier watch in 1906, there was a limited need for its functionality as a timing instrument over his 220-meter journey and 21.5 seconds of flight. However, as planes became faster and more reliable over greater distances, an accurate timepiece for the air navigation age was not just required, it was a necessity.

Alberto Santos-Dumont
Alberto Santos-Dumont had limited needs for a timing piece for his 21.5 second flight. A model bearing his name would soon be retailed and made famous by Cartier.

Planes, dirigibles, and balloons jockeyed for air supremacy, with the course of aviation history shaped forever during seventeen days in October 1910. Wellman’s dirigible America required a dramatic sea rescue after an unsuccessful Atlantic attempt, whilst Hawley and Post set a distance record in the Bennett International Balloon Cup, only to be lost in the wilds of Alaska.

The winner, the plane – after a nine-day aviation meet at Belmont Park, Long Island. Twenty-seven international pilots enthralled paying crowds who watched as speed, altitude and distance records were broken.  It ended October 27, with the very first ever race over a built-up area – around the Statue of Liberty, controversially won by the Frenchman, Henri Moisant.

Air-meet-1910-Lincoln-Beachey-in-a-Curtiss-design-with-the-crowd-in-the-stands John Garrett Collection.
Lincoln Beachey in a Curtiss designed plane from the Air meet of 1910 with the crowd watching in the stands. There was limited need for an aviator’s timepiece at this point in time. Post WWI few could see commercial aviation and the explosion in growth. Aluminum, increased engine capacity and reliability brought dynamic changes in this space and the need for a precise timekeeper as the world got smaller. Image John Garrett Collection.

The speed of the plane brought complex new navigational challenges. When traveling at 200 miles an hour, a kilometer is covered in just eleven seconds. Countries (including island fuel stops) quickly disappeared – bringing oceans, uncharted territory, and a risk to life if navigational calculations were wrong.

Longines chronometre awards

Just as Harrison’s quest for the mastery of longitude, sea navigation and his development of marine chronometers almost 200 years earlier, air navigation came to the fore.

Pilot’s lives depended on the reliability and accuracy of aviation timepieces and technical instruments as well as their ability to use them. Weems stated, “It is perhaps fortunate that timepieces were developed before radio, or else extremely accurate timepieces would probably never have been made”. [1]

Philip Van Horn Weems
The master of Air navigation, P.V.H. Weems.

Radio signal accuracy allowed perfect and easier time synchronization worldwide.  This expanded significantly in February 1924, when the British Astronomer Sir Frank Dyson developed the famous BBC “pips” using two mechanical Royal Observatory clocks which became known as the Greenwich time signal.

The grandfather of today’s GPS system and the backbone of this air navigation age was Lieutenant Commander Philip Van Horn Weems (1889-1979).  He was a pilot and master navigator who published a number of papers and books.

His Weems System of Navigation training courses were adopted by the US Navy, commercial airlines, Byrd, and Lindbergh after his Atlantic success.

Weems also devoted his lifetime toward improving instrumentation and navigation techniques for long distance flying.

Weems first navigation class equipment
The Weems system of Navigation was the backbone of aerial navigation, so called Avigation, for the better part of three decades and used by the military, commercial and later recreational aviation interests.

This remarkable time served as backdrop for the creation of the two most important aviator’s timepieces ever made: the Longines Weems ‘Second-setting’ watch which allowed for improved time synchronization, and Lindbergh’s ‘Hour-angle’ model simplifying longitudinal calculations. With just a pair of hands and a dial, a watch could be used to calculate gasoline consumption, ground speed, load-lifting capacity, tell time and navigate using celestial observations.

Longines Weems and Lindbergh

A Longines Weems & the improved Lindbergh Hour-angle watch

The Weems second setting watch was improved by Lindbergh who took up avigation training with Weems in 1928 after getting lost enroute over the Carribean. A few short years later in October 1931 the improved Hour-angle watch made famous by Lindbergh allowed easier avigational calculations.

Rear Admiral Moffett, who was the chief of the Bureau of Aeronautics for the US Navy Department stated “The suggestion… as to a moveable second-hand dial is considered to be a very valuable one, greatly facilitating the process of keeping a clock set to the exact time.” [2]

A rare and very special Weems watch, one of the very first delivered in April 1930, part of the very first batch of production pieces with the back marked BU. Aero Us Navy (Bureau of Aeronautics a US Navy department). The watch was just two serial numbers prior to the world’s very first Hour-angle watch born which was also the very first wristwatch ever made with a calibrated turning bezel.

Developed specifically for aviators with the Aircraft squadron’s battle fleet, it was officially designated as a “second setting navigation watch”[3] by the U.S Naval Observatory.  It was later distributed by them to the US Naval air stations and fleet along with filling private and government orders for the next twenty odd years.

Today Weems’s actual Longines ‘Aerochronometer’ as described in his 1931 Air Navigation book watch rests in the Smithsonian, absent its crown and is one of history’s most important pilot watches. 

First Weems prototype Smithsonian
The very first Longines Weems ever made, a prototype with serial 3585867 and the actual watch of the creator of the second-setting watch, P.V.H Weems. Image from the Smithsonian.

Adopted by Weems, the name and part of its function lies with the man Lindbergh described as the “Prince of Navigators,”[4] Harold Gatty.  He used it to describe a timing device which offset aircraft speed inaccuracies when making navigational observations. 

Weems’s ideas were first brought to life using modified Waltham Vanguard pocket watches prior to the arrival of the improved Longines wrist version.

A Waltham so called Vanguard pocket watch modified by Weems to make allowances for the second-setting function. This pristine unused example pays tribute to the challenges of mastering aerial navigation in the 1920’s and 30’s and enabled synchronization with a known accurate radio source or timekeeper. Weems started working with Longines on a wristwatch version and the first piece was delivered in November 1928. Image – Smithsonian.

Whilst little is known of the watch worn on his successful Atlantic crossing in May 1927, Lindbergh owned a modified Waltham Vanguard pocket watch and a hybrid Longines Weems hour-angle, pictured in the first issue of Weems Air Navigation book published in 1931. Six months later, the first turning bezel watch was born, a hybrid Weems/Lindbergh Hour-angle prototype.

Weems Lindbergh Hour-angle prototype, unit of arc
One of the prototype Hour-angle watches delivered to Lindbergh in April 1930 for testing. The unit of arc calibrations hand edited on the Weems dial. Image Air Navigation Weems first edition p399

The watch was a hand edited hybrid Weems of sorts, with a dial featuring notations for units of the arc and this was the precursor to the most famous drawing and watch in Longines history.

Weems wrote comments during publication that Longines were working on a graduated dial in arc, not time, along with “… a moveable bezel working on the same principle as the second-setting feature of the Aero Chronometer is fitted to the watch. The markings on the bezel are in degrees and minutes of arc only.” [5]

Lindbergh hour angle watch initial sketch

Heinmuller met Lindbergh shortly after he broke the US transcontinental speed record from Los Angeles to New York on April 20, 1930.  In a letter to his wife, he wrote “…I was privileged to work out details of his latest instruments with him as the enclosed design from him will show.  Keep it for our records. His latest ideas incorporate a second setting device for Greenwich Time, taken from the radio.  The device… permits laying down of a position in less than three minutes. Navy experts at Annapolis say it is the most outstanding aviation improvement in many years”. [6]

The hybrid watch, Weems, Heinmuller and the Longines technical team in St Imier were the formative pieces bringing life to Lindbergh’s famous 1930 drawings and delivery of Hour-angle prototypes in December 1930.  

Lindbergh commented he was examining the watch in a letter to Heinmuller in February 1931 and commented on its perfect timing in July. A patent request was filed for history’s most famous pilot watch, the Hour-angle, in October 1931. This watch, along with Lindbergh’s Waltham ‘Weems’ and a special Longines aircraft calotte have survived to this day and are some of history’s most important watches.

Lindbergh Weems Hour angle vintage watch. Unit of arc
A vintage Lindbergh Hour-angle watch in an all-silver case with a calibrated bezel with unit of arc readings enabling easier calculation of longitude.

The Hour-angle could calculate longitude, the hands giving you time in hours, minutes, and seconds, whilst the bezel and the inner chapter allowed you to establish your position in degrees, and units of the arc based on the bezel graduations and inner chapter markings.

Air navigation was a critical component to the progress, safety and the development of aviation as a whole. Accurate, reliable timing instruments were a critical part of establishing one’s position. This golden age of the aeroplane promised a shrinking world, bringing with it the challenges of duration and distance flights.

The rigors of flying at night over unchartered and unknown territory, with ever changing weather, and voyages over the sea created their own set of unique complex challenges.

Lindbergh's navigation tools on the Spirit of St. Louis
Some of the aviator’s navigational “tools” of the day in 1927 seem almost primitive when we consider today’s GPS system and our reliance upon it. It owes its roots to Weems who was the master of air navigation in the 1920’s and beyond.

In early aviation, two basic methods of early navigation existed. The first – ‘pilotage’, where known landmarks, rivers, mountains, and maps were used to assist at lower altitudes. The other, ‘dead reckoning’, included taking the last definitely known position and carrying forward with the last known speed, drift, course, and use of a compass.

To this, both radio and celestial navigation were added.

Longines Sidereal Time - 4
Longines were the very first company to recognize and provide wrist watches regulated for sidereal or star time in the 1930’s. They would almost always be used as a pair with another watch adjusted for civil time.

Heralding from the latin word ‘sidus’ meaning star, sidereal time essentially meant Star time, with a day measured according to the so called ‘fixed stars’, not set to the sun but relative to the other stars.

Sidereal time watches were regulated fast by 3min 56.6 seconds, with any adjustment noted in the archive for both Lindbergh and Weems models. Watches adjusted for sidereal time were most often used as a pair, for special missions with the other watch adjusted to civil time.

Wiley Post and Harold Gatty used a pair or Weems adjusted in this manner, creating history with their record breaking round the world flight in 8 days, 15 hours, and 51 minutes in June 1931.  Longines archives note their first use of a star on the dial to indicate sidereal time on October 25, 1932, and the Longines Weems was the very first sidereal time wristwatch.

A rare sidereal time Weems delivered in the mid 1930’s with the 18.69N calibre. The red stars indicating regulation for star time.

United States military celestial training schools run by Weems, Gatty et al in locations across America, such as Maryland and San Diego also taught large numbers of female navigators for the US military.

  These navigators existed in any of the following American military units WAVEs, WASPs and WACs who were often working in Ferry command. Amy Johnson, the first lady to fly from England to Australia noted that Weems was the best teacher in the world for celestial navigation on long flights.

In May 1937, Amy Johnson received celestial navigation training from Weems himself and took delivery of a special Sidereal time Weems watch that was delivered in February 1937. The watch has just been sold at Sotheby’s.

Longines played an incredible role delivering functional purpose-built aviation timepieces that helped shape safety and critical navigational calculations in the air age. They remained the dominant and pre-eminent player from the birth of the perhaps the very first wrist 19.73N chronographs delivered in 1911 likely destined for Russian aviation, right through to a purpose-built model for Swiss Air in the 1950’s.

Longines-vintage-weems-hour-angle, swiss-air-A-11 - 4356 - 4365-USNA
An accurate aviator’s timepiece was an essential tool watch at a time when mistakes and inaccuracies cost lives. Longines largely owned this space for the better part of thirty plus years. The models came in a variety of sizes, from the 27mm A-11 to the 47mm of the large Weems, Hour-angle and Swiss models which all used very similar cases.

The second setting watch allowed easy time synchronization with radio signals.  It was accurate, robust and highly functional. Lindbergh’s improved hour- angle watch of 1931, allowed for the easier calculation of longitude.   

Both models had a large 47mm case, enabling them to be worn over a flight suit, whilst the large onion crown allowed operation with gloves. Both the Weems second-setting watch and Lindbergh’s own hour angle watch could be regulated for sidereal time and an adjustment for same would be noted in the archives. 

Dramatic improvements in radio communication, radar and beacon technology radically changed aviation navigation just a few short years later.

Radio Navigation: “Flying the Beam” | Time and Navigation (

The famous slide rule features of Breitling’s first Chronomat ref 769 of 1946 would soon follow, whilst the famous Navitimer, in the early 1950’s.

[1] Air Navigation Weems 1931 first edition p399

[2] Air Navigation Weems 1931 first edition p400

[3] Air Navigation Weems 1931 first edition p400

[4] Terry Gwynn-Jones, ‘Harold Gatty: Aerial Navigation Expert,’ Aviation History Magazine, (World History Group, September 2001), (date accessed: 19/08/16).

[5] Air Navigation Weems 1931 first edition p399

[6] Man’s Fight to Fly John Heinmuller p75

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