Horology & Navigation: Understanding the IWC Mk. 11 Navigators’ Watch

One of the most influential Pilot’s watches of all time isn’t even a Pilot’s watch. IWC’s Mark 11 wristwatch was made for post-Second World War RAF bomber navigators and was rarely indued to the pilots themselves. Neither the premier manufacturer for the Mark 11, IWC, nor the watch’s other contracted manufacturer Jaeger LeCoultre (JLC), were behind the design at all. Rather, the case is borrowed from the previous British Armed Forces general service watch and the dial was specified entirely by the RAF. Despite this, IWC uses the design language of the Mark 11 from 1948 as the basis for a lot of their Pilot’s range today. In this post, I want to explore the Mark 11’s design and history by detailing three of its defining features: the outer case, inner case, dial and hands.

‘Dirty Dozen’ Outer Case

A defining feature of both the JLC and IWC Mark 11 is the use of a threaded ring behind the bezel which secures the crystal to the case. Not only does screwing down the crystal to the case stop it popping off under the low pressures of flying at altitude, but also prevents particles and dust entering the mechanism.

The threaded ring is a design feature which was probably first used in military timepieces by the British casemaker Dennison, who had made cases for Rolex, Tudor, Longines, JLC and IWC among others. Dennison had a close relationship with the British Armed Forces during World War One and word of mouth has it that they first used this screw-back crystal design on military pocket watches at this time. It is also worth noting that during World War One, the director Author Dennison actually served as a pilot in the RAF.

The Dennison screw-in crystal design was adopted by the British Military for the General Service wristwatch during the Second World War - the w.w.w. (standing for waterproof wrist watch) - colloquially known by collectors as the Dirty Dozen since 12 manufacturers were commissioned to produce the watch.

The evolution of the Mark 11’s 37mm case can be seen in the fact that JLC’s version uses the same case as the JLC w.w.w., and the IWC Mark 11 uses a case almost identical to the Record w.w.w., albeit in solid stainless steel as opposed to plated brass in the case of the Record. As a result, some fake IWC Mark 11s go as far as to make use of a cheaper Record w.w.w. case.

Soft Iron Inner Case

The mechanical watch, like many other components of a mid-century bomber aircraft, is prone to magnetism. Magnetism can be curbed by the use of iron, so components like the radar cathode of an Avro Vulcan bomber were given an outer antimagnetic screen, and so too was the Mark 11. Only in the case of the Mark 11, a soft iron housing was used inside the watch to cover the movement rather than on the outside. Most readers will be familiar with the iron cap seen behind the caseback covering the movement, which appears on several antimagnetic watches of that era. Though the Mark 11 went a step further, making use of both an iron ring holding the movement and the dial itself made of iron to surround the movement on all sides. All three components - the intermediate iron caseback, movement holder and dial - enclose the movement in soft iron, acting like a faraday cage to repel magnetic fields onboard the aircraft.

The antimagnetic iron cage was not new in the case of the Mark 11. The Parisian brand L. LeRoy & Cie is probably the first military contracted manufacturer of a soft iron inner cage for pocket watches produced for the Royal Navy in around 1910. The first patent for a soft iron inner case seems to be for Giles Bros. in 1884.

For IWC, the inner iron cage became a major selling point for their Ingenieur as well as Pilot’s series watches.

Dial and Handset

If you take a look at the Pilot’s range from IWC today, you’ll see black dials, white numerals and often a triangle at 12 o’clock. This language is the offspring of three major military aviation watches in the IWC archive:

(1) the Mark IX, first produced in 1935;

(2) the 55mm ‘B-Uhr’, first produced in 1940 for Luftwaffe pilots and navigators;

(3) the Mark 11.

The dial of the Mark 11, like the Mark IX before it, was specified through-and-through by the RAF. It started in 1948 with a numeral at 12 o’clock - nicknamed ‘white 12’ by collectors - which was changed by specification of the RAF in 1952 for a triangle for greater legibility. Most of the original ‘white 12’ dials were changed out for triangle ones during service, which was regular for military kit, so to find an original one is quite rare. From 1963 the dials featured an encircled ‘T’ to denote the use of tritium luminous paint. From 1952 to 1963, the encircled ‘T’ was added to the dial post-production by the RAF themselves, and so is a messier print than the rest of the numerals. IWC made service dials in the 1990’s which have a clean ‘T’ which are less desirable to collectors. The 7 on the dial was sometimes hooked at the end, but original ones are exceedingly rare; if you see a hooked 7 it is probably a service dial made by IWC in the 1990s. Some fake dials made for watches which were never given a dial exist, but these are easy to spot since they are made of brass rather than iron. Some white dials have been recorded, made of iron and featuring a ‘messy T’. These white dial versions are extremely rare and are rumoured to have been modified for use on Royal Navy submarines, but these are just rumours and these examples could be faked for all we know.

The hands of the Mark 11 were originally syringe-shaped, but the hour hand was changed to a squared-off shape somewhere around 1952 for legibility. Like the dials, IWC made and fitted service hands in the 1990’s which can be spotted since the original ones’ lume forms a triangle at the base of the hands, whereas the service ones are squared at the base (you have to look very closely for this detail).

So while the Big Pilot today is clearly inspired by the B-Uhr from 1940, IWC’s other Pilot’s lines like the Mark and Spitfire series take their dials, hands and relative size from the Mark 11.