Through much of World War II, allied aviators were donning the American-made A-11 service watch.  While this tough-as-nails timekeeper performed meritoriously for soldiers and airmen alike, Britain's Ministry of Defense found that the production specifications of the A-11 were too broad and resulted in timepieces too imprecise for effective navigation.

As an answer to the A-11, the MoD issued new standards for the watches going to its RAF pilots.  The new standard, coded 6B/346, required chronometer-grade performance and anti-magnetic properties.  For the production of this new timepiece, the MoD turned to major European manufactures, eventually giving contracts to two: International Watch Company and Jaeger-LeCoultre.

The resulting timepiece was the Mark XI Pilot's watch.

In addition to the relatively standard features present on the A-11 (center seconds, hacking and a stainless steel case) the Mark XI featured a soft iron dial and dust cover which shielded the movement from magnetism.

While IWC produced their version of the Mark XI with their existing Calibre 89 (which found its way into many IWC models of the era), Jaeger-LeCoultre filled their orders with a 12.5 ligne, 16-jewel Calibre 488SBr movement - a movement that was only used in the Mark XI series - making the JLC executions much more sought after by collectors.

This particular example was produced in 1948 and features the original JLC dial, hands, crown and "Staybrite" stainless steel case.