The appeal of IWC & Jaeger-LeCoultre's masterpiece military watch, the Mark XI

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Vintage military watch Mark 11 mk.11 IWC Jaeger-LeCoultre

Perhaps no other wristwatch in history embodies the meaning of a "practical watch" better than the Mark 11.
Produced by IWC and Jaeger-LeCoultre to specifications required by the British Ministry of Defence, the Mark 11 was designed from the ground up with a focus on functionality and practicality.
As a result, the Mark 11 became the gold standard for pilot watches, influencing numerous designs since its creation in 1949.
Let's take a closer look at this historic piece.

Mark XI Mark 11 Military Watch

What is Mark 10?

In the early 1940s, the British Ministry of Defence created a list of specifications required for a military watch.






・Jaeger LeCoultre







Twelve companies were allowed to manufacture watches based on those specifications.
The resulting watches were known as the "Dirty Dozen," or more specifically, "Mk. X," and are still highly valued by collectors today.
W.W.W. Dirty Dozen Military Watch

What is Mark 11?

The watches issued under the name of the Dirty Dozen were approved for military use, but were not accurate enough for aviation.
As a result, in 1946-47 the British Ministry of Defence set new standards for watches for aviators.
This is the watch called “6B/346” or “Mk. 11”.

Mark 11 specs

Mark XI Mark 11 Specifications
The following specifications were required for the Mark XI:
First, the matte black dial features Arabic numerals numbering from 1 to 12.
The minute markings were to be white, with the bolder markings at 3, 6, 9, and 12 o'clock having to be luminous.
Next, the use of high-performance Swiss-made movements was made mandatory, with a size of 12 lignes (approximately 27 mm), a power reserve of 36 hours and an average daily deviation of -4/+4 seconds.
It also needs to have a Glucydur balance, a Nivarox balance spring, and a central seconds hand with a hack function for synchronization.
The case is waterproof to a depth of 20 feet (about 609 m) and uses a Faraday cage to prevent magnetism.
The acrylic wind shield must be secured in place with a set screw to prevent separation due to reduced pressure.
Vintage military watch Mark 11 mk.11 IWC Jaeger-LeCoultre

The Bonklip stainless steel bracelet (model number 6B/2763) had to be secured to the case.
The Ministry of Defence took this specification list to Goldsmiths & Silversmiths, a UK-based jewellery store.
Goldsmiths & Silversmiths searched for a manufacturer to produce a watch that met these specifications, and ultimately chose IWC and Jaeger-LeCoultre.
Once completed in 1949, the Mark 11 was supplied to the Royal Air Force, the Federal Aviation Administration, the Royal Australian Air Force (RAAF), the Royal New Zealand Air Force (RNAF), other services and eventually private companies.
Before being delivered, every watch goes through rigorous performance testing.
The watch is adjusted over two weeks in the Royal Observatory's chronometer workshop at Herstmont-Ceilles to withstand five different positions and a range of temperatures.
Furthermore, to maintain this performance, the products were retested annually even after delivery.

Mark XI design

Mark XI Mark 11 Side

The specifications set by the British Ministry of Defence were so strict that the Mark 11s produced by IWC and Jaeger-LeCoultre are very similar in both construction and appearance.
Both cases are made of stainless steel and are almost identical in size, with the IWC at 35.98mm in diameter and the Jaeger-LeCoultre at 35.3mm.
Both have long lugs to which the spring bars are fixed.
The dial is cup-shaped and has a steel back or a Faraday cage to make it anti-magnetic.
Both Mark 11s were produced during the same period when IWC and Jaeger-LeCoultre were commissioned, and although they are similar, there are a few differences, such as the markings on the dial, hands, and case back.
The Mark XI's design has changed significantly several times over time.
For example, the early Mark 11 did not use a triangle mark as the 12 o'clock index, but instead had two dots on the Arabic numeral "12."
The design was changed around 1952 to improve the legibility of the watch.
Similarly, the hour hand was short and squared off for better legibility (this is now a distinctive design for the IWC Mark Line).
IWC Mark 11 watches manufactured after 1962 feature a circled T above 6 o'clock on the dial to denote the use of tritium.
Around this time, the British Ministry of Defence also began replacing existing radium watches with tritium.
However, the RAAF and RAF did not require radium replacement, so these watches are not marked with tritium.
The Bonclip bracelet was discontinued and a few years later was replaced by a nylon NATO strap (model number 6B/2617).
Mark XI Mark 11 Back Cover

The dial, case and movement of the Mark 11 are marked with the Broad Arrow mark, signifying that the watch is government property.
Similarly, the model number "6B/346" is stamped on all Mark 11s.
The "6B" indicates that the product is for aviation, including products other than watches, and the number "346" indicates the order in which the model was made.
In addition, each watch is marked with a serial number and the year it was ordered. For example, "2283/51" would indicate that it was the 2,283rd watch ordered in 1951.


Mark XI Mark 11 Movement

The Jaeger-LeCoultre Mark 11 is fitted with a highly accurate chronometer-certified movement called the Jaeger-LeCoultre Caliber 448/Sbr.
This caliber was produced in limited quantities for a limited time and later became the basis for the caliber P478/BWSbr used in the iconic JLC Chronomètre Geophysique made in 1958.
The IWC Mark 11 is fitted with the caliber 89, renowned as one of the most robust three-hand movements ever made.
Caliber 89 operates at 18,000 bph and features a Breguet hairspring and a patented indirect drive to power the central seconds hand.
After a while, an Incabloc shockproof device was installed to improve shock resistance.
Jaeger-LeCoultre's Mark 11 was discontinued in 1953 due to its poor shock resistance.
A total of approximately 2,950 watches were produced for the Royal Air Force and the Royal Australian Air Force, but all of them were withdrawn from use in the 1960s.
IWC subsequently became the sole manufacturer of the Mark 11, producing nearly 8,000 examples between 1949 and 1953.
Although the Mark 11 was completely phased out in 1981, approximately 1,000 examples were sold commercially between 1973 and 1984.
The Jaeger-LeCoultre Mark XI was never sold for commercial purposes.

Mark 11 Various variations

Mark XI Mark 11

There are still many vague points about the Mark XI, so we won't go into detail here, but one of the reasons it has become so complicated is that various improvements and fine-tuning were made during the production process.
The fact that different organisations had different specifications (for example, the RAF required the Broad Arrow marking on the dial, while the RAAF did not require this marking) was another factor that led to the many small variations that came about.
Furthermore, there are a wide variety of variations, including compatible IWC cases and movements, and models with NOS dials and hands, but if we were to introduce one wonderful product among them, it would be the one shown in the photo, which was supplied to the Royal Air Force.
This product is an iconic design of pilot's watch, and influenced various later designs, such as the Mark 12 based on Jaeger-LeCoultre and the Mark 15 equipped with an ETA movement.

Mark XI Mark 11 IWC

Today, the Mark 11 is a highly regarded piece of military heritage.

Ten years ago, even a good-condition piece could be purchased for around 200,000 to 300,000 yen, but nowadays a single piece can go for at least 800,000 yen.

A great masterpiece with a long history, the Mark XI is one of those products that every watch enthusiast should know about, whether they want to own one or not.


The Mark 11 was an even more accurate version of the Mark 10 and was made for pilots.
It's easy to understand why the still-famous Jaeger-LeCoultre and IWC were able to meet the British government's conditions.

Although the Mark 11 watch is a wonderful piece, the number of pieces made is very small. Therefore, even though it is a wonderful watch, it is difficult to get your hands on one.

If after reading this article you are interested in purchasing the Mark 11, please feel free to contact us.

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Vintage military watch Mark 11 mk.11 IWC Jaeger-LeCoultre