The Jaeger LeCoultre Mark XI
Francis Chang <francis@francischang.com>

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Contents

Specifications - A summary of the key facts
A Photo Essay - The Story of a Mark XI
... Part 1 - The Joys of Opening the Mail
... Part 2 - Regulating a Watch

References

Specifications

Manufacture:	Jaeger LeCoultre
Model:	6B/346, G6B/346, JLC E161
Caliber:	JLC 488/SBr
Water Resistance:	10 meters
Dimensions:	34.7mm case (without crown), 38.4mm case (with crown), lug-to-lug 43.5mm, height 12.6mm, 17.0mm lugs

Notes:
• 16 jewel hack set caliber 488 SBr, 18000 vph SBr = Stop (hacking), Breguet overcoil Movement has a height of 5mm with a diameter of 28.8mm.
  Single bridge design for the motion train
  Rhodium brass finished with 6 Geneva Stripes (IWC Mark XI has 9)
  Mainspring length 420mm, width 1.28 mm, thickness 0.1275 mm
  Balance wheels are uncut self-compensating screw balances with Nivarox breguet overcoils, and lacks balance shock protection.
  Indirect drive sweeps seconds
  Movement serial typically 59XXXX on RAF 48, 91XXXX on RAAF 53
• The crown release is the screw closest to the crown
• Orange radium dial/hands
• Some watches had fixed lugs (usually RAF), while other had spring bars (usually RAAF)
• “6B” means “Flying Equipment”, “6B/346” is the watch specification number, noone know what the “G” means
• “E161” is JLC's internal reference number
• “B/97” sometimes appears on the caseback of the RAF model. Noone knows what it means.
• Antimagnetic dust cover made of soft iron encloses the movement, protecting it from magnetic fiels.
• screw back case
• oversize crown, sometimes appearing with the JL logo
• Goldsmith & Silversmith Ltd. was the broker between JLC and IWC. G&S contracted the production of the Mark XI, and distributed finished watches to RAF and RAAF.
• JLC, IWC, Longines and Omega all had watches that met the Mark XI specificiation
• luminous markers at 3, 6, 9, 12
• 5 dial variants (3 RAF, 2 RAAF). Broad arrow on dial was most likely added after coming from JLC. (Possibly G&S or Ministry of Defence) JLC has run out of NOS variations of my dial.
• 3 Hand styles: cast faux-cathedral hands, tapered hour & minute hands, Squared hour with tapered minute hand (Similar to IWC Mark XI)
• Only 2700 ever made, issued in two batches. An RAF batch in 1948, and an RAAF batch in 1953 (aprox 2000 RAF, 700 RAAF)
• William Gibson's favorite watch, featured in the novel, “All Tomorow's Parties”
• Overheard: The Ministry of Defence applied the luminous stuff to the dial.
• On the back, the XXXX/48 or YYY/53 indicate the serial number/year
• My Mark XI has unusual hands (I've never seen this variation before). The hands are longer than most, and there is less radium on my hour hand. Also, it has an unusual circular finish on the caseback (this has been seen before), and has spring bars instead of fixed lugs, which is unusual on the RAF variation.

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Story Part 1 | Story Part 2 | Timepieces Home | References

- Francis 2003