With IWC Extract from the Archives confirming the sale of the present watch on 21 February 1945.
In the early 1940s the British Ministry of Defence selected 12 watch manufacturers for the supply of wristwatches for their armed forces, amongst them IWC. The watches had to feature a black luminous dial with subsidiary seconds, a 15 jewels movement, a waterproof lever higher than normal and a case capable of diminishing the results of shocks. The backs of these watches featured the engraved specification "W.W.W." for Watch Wristlet Waterproof.
The W.W.W. models, made by the 12 different manufacturers were nearly identical, however only IWC used a snap on back instead of a screw back but a lead seal between case and case back prevented the penetration of water into the watch.
IWC produced a series of 6000 examples of the Mark X mode, the cases numbered from 1131001 to 1137000, all with calibre 83 12'''movement. The circular water-resistant stainless steel cases had fixed soldered pin bars, the backs were engraved W.W.W. and with the Broad Arrow, indication that the watch is owned by the British Crown. The 5 digit number after the "M" represents the individual serial number, the "M" indicates IWC as the manufacturer (Omega for example used the letter "Y"). By subtracting the M-number from the case number, the result is always the figure 1118980.
The inside of the case backs were engraved with the Broad Arrow symbol, W.W.W., case and serial numbers, oval IWC stamp and "stainless steel".
Unlike the Mark XI (or 11), the Mark X (or 10) was supplied to the Royal Army and not to the Royal Air Force.