JLC Mark XI Pilot's Watch

JLC Mark XI Pilot's Watch

From the earliest days of aviation, watch manufacturers endeavored to develop a timepiece that would allow a pilot to calculate his position at a glance. In 1929 Longines produced a "seconds-setting" watch designed by Philip Weems, a professor from the U.S. Naval Academy. Longines also produced the Hour Angle in 1932, with insight from one of the most renowned aviators to ever take to the skies, Charles Lindbergh.

Like Longines, IWC was among the first brands to establish itself as a manufacturer of aviation watches, starting with the first watch ever developed solely for aviation: the Spezialuhr für Flieger or Special Pilot's Watch, in 1936. But as aviation became militarized, the importance of watches as navigational tools increased. In 1948 the British Ministry of Defense called upon manufacturers to design watches that could meet the rigorous standards required for military use. 

As an answer to the A-11, which was then standard issue for pilot's watches, the MoD issued new standards for the watches going to its RAF pilots. This 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, and the resulting timepiece was the Mark XI Pilot's watch.

To ensure that the watch met the requisite anti-magnetic properties, 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 theirs with a 12.5 ligne, 16-jewel Calibre 488SBr movement. The Calibre 488SBr, which had its beginnings at a modification of the calibre 470, was only used in the Mark XI series, making the JLC executions much more sought after by collectors. Another interesting note about the calibre 488SBr is that a subsequent revision, the Calibre P 478 BWSBr, would later power the Geophysic

The Ministry of Defense spared no expense in guaranteeing that the watches maintained their accuracy. Each watch was subjected to a 44-day testing period at the Royal Greenwich Observatory, which included 14 days in which the watches were tested in five different positions and at two different temperatures. Once the watches passed these rigorous tests, they had to be returned to the Royal Observatory for testing within a year. 

The Mark XI entered military service in 1949 and was decommissioned in 1981. This stunning example was produced in 1948, and its size (slightly small by today's standards) belies the sturdiness and dependability of this robust navigating machine. Reliable to the last, it exemplifies the truest notions of a tool watch. 


Stainless steel case is approximately 35mm (excluding crown). JLC Reference E.161 6B/346, cal. 488SBr Manual-Winding Movement. Circa 1948.

Overall Condition: Stainless steel case is in very good condition with only minimal signs of wear and use, including some light scratches visible on the case. Dial is in very good condition with fine overall patina on the luminescent elements of the hour markers and syringe hands. Unsigned crown; screw-down case back bears military engravings "6B/356, 3233/48."

Includes one 18mm black leather pilot-style strap and two 18mm nylon straps from Crown & Buckle

SKU: AS01516

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