Definition and development of the military deck clock / observation clock internationally

An observation clock, also known as a B-clock or deck clock A pocket watch is a portable watch designed for navigational purposes. Observation watches required an official certificate. 

Similar clocks were also used in astrometry and astrogeodesy until around 1970, where they acted as an intermediary between the measuring instrument and the time signal and were called working clocks .

The construction of this type of watch, which was designed as a portable precision watch primarily for navigation purposes, had to meet the following criteria :

• High-quality movement
• High-quality escapement
• Compensation of the gear regulator
• Large dial , clear display

The era of high-performance marine chronometers began around 1780. These clocks were mounted on gimbals due to the positional sensitivity of the escapement system.

Some reasons that accelerated the development of a portable precision watch

• Before embarking on a sea voyage, the marine chronometer had to be synchronized with the local time in the harbor, where the longitude was known. To do this, the time had to be brought to the ship from the nearest observatory , where precise timekeeping was carried out on an astronomical basis. The precision pendulum clock set up in the observatory was, of course, stationary. Accurate, small, portable clocks were needed to "transport time" between the observatory and the ship. The chronometer could not be set or adjusted. Therefore, only the difference between the marine chronometer and the time brought on board was recorded in a book.

• The process of determining longitude on board was not easy. A small, accurate, portable clock was necessary, especially for sailors, who were not solely dependent on the ship's built-in chronometer but could use the deck clock or observation clock at various points on deck to perform calculations and measurements—i.e., observations —to determine the ship's position.

• The numerous research expeditions taking place during this period also required accurate, portable clocks for precise geographical location and time determination. ^{[ 7 ]} These clocks were called pocket chronometers or precision pocket watches. Alexander von Humboldt used a Breguet pocket chronometer on his American expedition (1799–1804). ^{[ 8 ]}

The development of this type of watch is therefore closely related to the actual marine chronometers and the observation watches were manufactured by the same watchmakers or companies.

See also: Astronomical navigation , Longitude problem (Historical) , Longitude clock

In the first half of the 20th century, the largest number of B-watches were manufactured for military purposes.

From this period, observation clocks can be divided into three subgroups: ^{[ 9 ]}

1. Chronometer watches (pocket chronometers)
2. Deck clocks
3. Precision watches

The table shows the classification of watches in three European countries.

observation clock	German Empire	England	France
1. Chronometer watch	B–clock 1st class	Chronometer Watch HS2	Board chronometer Torpilleur Watch
2. Deck clock	B–clock II. Class	Deck Watch HS3	Counter
3. Precision clock	B–clock III.Class	Deck Watch HS4	Counter

Observation watches were widely used until the end of the Second World War and continued to be used in the navy afterward.

Based on the requirements for observation watches for the German Air Force formulated by the Reich Air Ministry in Fl. 23883, various manufacturers were required by resolution in 1940 to start production according to strict specifications. ^{[ 10 ]}

During the war years, the following manufacturers produced pilot observation watches:

• IWC , Schaffhausen
• Stowa , Engelsbrand
• Wempe , Glashütte
• A. Lange & Söhne , Glashütte
• Laco , Pforzheim

It is falsely claimed that historical aviator observation watches were worn by pilots. Instead, they were worn by onboard navigators who, in combination with an octant (protractor), could determine the aircraft's exact position. The pilots themselves usually wore chronographs, such as those from Hanhart or Tutima , as a backup in case an onboard clock failed.

Observation watches and wristwatches had several typical features: The exact specifications for the B-watches according to construction instruction Fl. 23883 of the Reich Air Ministry (RLM), for example, called for a large diameter of 55 mm and a large onion-shaped crown so that navigators could operate the watches even when wearing gloves. There are two models of aviator observation watches: Model A had inscriptions for the hours 1 to 11 in Arabic script. Instead of the "12" there was an outward-pointing triangle with two dots. This is also the case with Model B, except that instead of the Arabic numerals 1 to 11, the minutes are printed in increments of 5. The classic hour division from 1 to 12 is located on an additional inner ring.

The number of the construction instructions (Fl 23883) is engraved on the edge of the case and on the case back of the historic observation clocks. The manufacturer, model, device number, and movement designation were also inscribed on the steel case back. ^{[ 11 ]}

The decline of the B-Uhr only came in the second half of the 20th century with the invention of the quartz clock , whose accuracy improved by three orders of magnitude . The B-Uhr thus lost its raison d'être as a navigational instrument. Today, ships use GPS (Global Positioning System ) for navigation, but means for determining positions using astronomical methods (i.e., tables and instruments) are still required.

To this day, observation watches are manufactured by various manufacturers for collectors and enthusiasts. ^{[ 12 ]} As a result, the term "observation watch" has been extended from the pocket watch to the wristwatch . ^{[ 13 ]}

Deck watches from the 20th century demonstrate the full range of technical developments in watchmaking. The movements were manufactured with great precision and usually mounted on 16 to 22 jewels . The predominant escapement is the lever escapement . English watches use the spherical lever escapement , while all others use the Swiss lever escapement . Watches with chronometer escapements or tourbillons were only experimented with. The regulator is always of excellent quality and temperature-compensated.

Clear legibility of the indications and numbers was always part of the specifications. Roman numerals were preferred until World War II, and later Arabic numerals . For deck watches, which were to be used instead of marine chronometers, a power reserve indicator was also required. 

Cases for deck watches are generally simple, solid, and functional. They are modified to suit the watch's function, e.g., with extended pushers for setting the hands, omission of the crystal, etc. Most 20th-century watches have nickel alloy or stainless steel cases. Silver cases were rarely used.

Only American deck watches were equipped with a three-part wooden case, like a marine chronometer. Other procurement agencies were content with simple padded wooden cases or brass boxes.

The procurement policies of the individual states varied considerably. However, all of them cut costs on technically unnecessary equipment. Procurement authorities bought precision and accuracy, not beauty. ^{[ 15 ]}

Cortèbert – Switzerland International Watch Company – Switzerland LACO (Lacher & Co.) – Germany A. Lange & Söhne [ 16 ] – Germany STOWA – Germany

Wempe – Germany (with Swiss movement by Thommen) Ulysse Nardin – Switzerland Vacheron & Constantin – Switzerland GUB (VEB Glashütte Watch Factory) – GDR

Despite great efforts, Germany remained dependent on watches from Switzerland.

Maurice Ditisheim – Switzerland Elgin National Watch Co. – USA Hamilton Watch Company – USA Hornby – England L. Leroy – France Longines – Switzerland Patek Philippe – Switzerland

Roskell – England South Bend Watch Co. – USA Ulysse Nardin – Switzerland Vacheron & Constantin – Switzerland Waltham Watch Co. – USA Zenith – Switzerland

First Moscow Watch Factory – USSR

J. Auricoste Breguet – Switzerland P. Buhrè – France International Watch Company – Switzerland

L. Leroy – France E. Thomas Ulysse Nardin – Switzerland

Alexander & Son – Coventry Ashley – Clerkenwell , London Austin & Williams Baird – London Birch & Gaydon – London Brockbank & Atkins – London Buckney – London Carley & Clemens – London George Carley – London Connor Cuthbert – Glasgow Cribb – London Erhardt – Birmingham Elgin National Watch Co. – USA Dent – London French – London Frodsham – London Golay & Son – London Glover – London Goddard & Co. – London Hamilton Watch Co. – USA Halford – London Hall-Louth Hall Bros. – Liverpool Hamilton & Inches – Edinburgh Hammersley – London Hughes & Son

Isaac – London Iversen – Bergen , Norway Johannsen & Co. – London Kendal & Dent – London Keys – London Lilley & Son – London L. Leroy – France Longines – Switzerland Lindquist – London Lister – Newcastle Lockwood Lund & Blockley – London Kullberg – London Kunzler – Birmingham Mc Kabe – London MacKay & Chisholm – Edinburgh Matthews – London Thomas Mercer – London Milne – Manchester Murray & Strachan – London Newsome & Co. – Coventry Northern Golrsmith Ltd. – Newcastle Ollivant & Botsford – Manchester Page & Keen – Plymouth Parkinson & Frodsham – London Player & Son – Coventry Philips – London