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The Cabot Watch Company is arguably the best-known maker of British military watches. It was founded in 1972 and produced watches for a number of different applications suited to the varying demands of the different branches of the British armed services. The most ubiquitous of these is the G10, a general issue service watch produced in large numbers from 1980 until the present day. CWC estimate that about 200,000 of these watches were produced from 1980 until 2008 and were used by the British Army, Royal Navy, Royal Air Force and Royal Marines.

The G10 was the first quartz watch issued to the British Armed forces and through its 28 year life as an issued watch, the thickness of its case tracked the bulk of the movements housed within. The earliest watches were fitted with the ESA 536.121, whose thickness warranted a mid-case of suitably generous girth.

Those early watches were subsequently nicknamed ‘Fatboy’ in recognition of their bulk compared to the slimmer case designs that were to follow. The G10 Fatboy was produced from 1980 until 1983, with a change in dial logo from no oval logo to the current oval logo style in 1982. In 1983, the movement was changed from the ESA 536.121 to the Marinium–branded ESA 947.111 seven jewel movement. The reduction in thickness of this newer, higher grade movement was recognized in a slight slimming of the case from 13mm to 11.8mm, measured from the domed acrylic crystal to case back.

The third variation appeared in 1984/85 with a change in movement from 947.111 to 555.112 but retaining the same case. The fourth and final version released in 1987 featured a much slimmer 10.2 mm case fitted with the ETA/ESA 955.114 (and variants). I’ve written about that model before but the present post concerns the first two variations on the Fatboy theme.

I am in the position to write about these watches because back in October, a reader of this blog asked if I would be interested in trying my hand at a Bulova Accutron and if so that he would be willing to donate it to the cause. I gratefully accepted and when opening the package that he subsequently sent me, discovered a bonus of three crocked CWC G10’s in addition to the Accutron. In recognition of that generosity, this post is dedicated to Simon. Thank you!  Here then are those three watches, all British Army issued:

The watch to the right is a ‘Fatboy’ G10, fitted with the ESA 536.121 and dating from 1982. The watch in the middle is a fit Fatboy, fitted with the Marinium 947.111 and dating from 1983. The watch on the left is also a Marinium watch but this one dating from 1984. Three British Army G10’s spanning three years from 1982 to 1984.

All three watches were non-functioning but for different reasons. Initial diagnoses required some investigative probing courtesy of my Horotec Flashtest.

Herewith then a summary of the ills that affect each:

  • 1983 947.111: Coil fine (2.5 kΩ impedance); Circuit dead;
  • 1984 947.111: Coil dead; circuit fine but the quartz oscillator AWOL;
  • 1982 536.121: Coil fine, circuit ok but no action whatsoever.

For no logical reason other than that this is the order in which I tackled the three, we begin with the older of the two Marinium watches.

Externally, this is probably the sweetest of the lot, at least from the front. The tritium on the dial indices and hands is that perfect honeyed hue of 35 year old tritium lume.

The rear of the watch is comfortably the most grot-encrusted of the three but provides an opportunity to refresh our understanding of the rather perplexing stock code system.

The code shown above comprises four parts:

  • the first is the MoD stock code which identifies the branch of the armed forces to which the watch was issued. W10 is British Army, 0552 Royal Navy, 0555 Royal Marines and 6BB Royal Air Force and so clearly in this case we have a British Army issued watch.
  • The 13 digit number that follows is the NATO stock number (NSN). The first four digits are the NATO Supply Classification Group (NSCG) code that relates the item to a NATO Supply Group (digits 1 & 2) and a NATO Supply Class (digits 3 & 4). In this case, 66 refers to Instruments and Laboratory equipment and the 45 refines that to Time Measuring Instrument.
  • The next 9 digits make up the NATO Item Identification Number (NIIN). The first two digits indicate the assigning country’s National Codification Bureau (NCB) code which, for the UK is 99. The final seven digits are randomly allocated and indicate the code number for the unique item in that country’s inventory. In this case, 5415317 refers specifically to the CWC quartz-powered general service issue watch.
  • The final two digits refer to the date of issue and so we infer in this case that this watch was issued in 1983.

The movement looks ok at first glance:

We recall though that this watch is afflicted with a non-functioning circuit. To get to the bottom of that diagnosis, we need to remove the movement and that first requires removal of the substantial case ring.

The case ring is not attached to the movement, having been held in place by a (now absent) rubber gasket sitting around its periphery. Turning the extracted movement over provides a view of the immaculate dial, together with a set of hands showing just a hint of encroachment of degradation around the edge of the lume.

The dial feet are secured to the movement by friction alone and so, with the hands removed, the dial simply levers away from the movement, revealing a completely intact calendar.

It is a little curious that the calendar functions have been retained in a watch with no date aperture in its dial but perhaps simply a sign of the economic imperatives in the contract to assemble these watches. Turning the movement over and removing the train bridge and we get first sight of one of the reasons why this movement may not have been functioning:

A whopping great clod of fluff caught up in the train wheels. However, a more compelling clue lies in surveying the third wheel pinion:

The tell-tale signs of blue/green copper salts suggests a historic battery leakage which in turn would explain the apparent expiry of the integrated circuit (IC). On this movement, the circuit is located beneath a plastic cover on the train side.

Those spider legs look incredibly vulnerable but it is not mechanical trauma that has afflicted this circuit but chemical. You should be able to see the encrustation around the base of the integrated circuit that has developed from the leakage and flow of battery electrolyte. This circuit has passed on. It is no more. It has ceased to be. It’s expired and gone to meet its maker. It’s a stiff. Bereft of life, it rests in peace! Its metabolic processes are now ‘istory!*

Given the pronouncement above, the next question then is whether there is some means to transplant a healthy replacement IC. Well, the answer to that is no. The integrated circuit is hard-wired into main electrical circuit that is permanently encapsulated in the plastic main plate.

There is no salvation for this movement and so we consign it to ‘istory and seek out alternative remedial measures. Notwithstanding the in-built disposable nature of this particular calibre, I would rather retain some degree of originality in specification and so seek out a source of old stock ESA/Marinium 947.111 movements. These, it turns out, are relatively easy to source cheaply and so, anticipating that the 947.111 fitted to the second watch may also not be salvageable, I order two new old stock replacements from a Swiss seller on eBay.

On one of these, the plastic cover over the IC has become detached which provides an opportunity to look at what the IC should have looked like in the defunct movement.

I don’t propose to perform any service work to either of the Marinium 947’s, notwithstanding their presumed age, because the current draw on both is exactly within specification with the movements running.  We are not yet on the home straight though because the mid-case needs a clean and I need to think about what to do about the crown gasket, which is partially captured by the crown.

Case cleaning proceeds with the aid of wooden toothpick, ultrasonic bath and toothbrush.

We need to confront the slightly thorny issue of consumables with this watch. OEM crystals and gaskets are not so easily sourced – in fact I do not believe that the original gaskets are available from any source and extracting crystals from Silvermans (the current UK owner of CWC) is not especially easy. However, I can draw on my experience from last time working on a later example of the G10 and do have the benefit of a full set of used gaskets from which to take measurements.

Starting with the crystal, my experience suggests that a slightly oversized Sternkreuz 31.7mm armoured acrylic should provide an extremely snug fit; the 31.6mm crystal commonly recommended does not fit so securely in this and later cases, being freely rotatable once fitted. In order to inject a soupçon of je ne sais quoi, I opt for a high dome 31.7mm acrylic and reuse the original sandblasted tension ring.

This second generation Fatboy employs two case back gaskets, one sitting around the case ring and the other acting to secure the case ring into position by forming a compressible seal to the centre of the case back. There is also a smaller gasket that sits around the battery hatch and, of course, the encapsulated crown gasket. My measurements, combined with some trial and error, yields the following:

  • Outer case back o-ring: 29.8 mm x 0.6 mm (ID x cross-section)
  • Inner case back gasket: 28.5 mm x 30.0 mm x 0.5 mm (ID x OD x thickness)
  • Battery hatch: 12.0 mm x 0.6 mm (ID x cross-section).

I did try a 0.7mm cross-section outer case back o-ring but failed to get the case back to seat so 0.6 mm it is.

The crown gasket is notionally somewhat awkward to extract given that it sits behind a permanently fixed washer. However, there is a reasonably generous gap through which some gentle probing with a used oiler eventually liberates the gasket.

I tried three different sizes of replacement, eventually settling on 2.3mm ID x 0.6mm cross-section o-ring.

The only slightly awkward element of fitting the dial and hands to one of the new movements is the usual business of getting the seconds hand to align with the minute markers.

With this movement, there is a little drift as the seconds hand makes its journey around the dial with some quadrants bang on and others a tad off but nothing to lose sleep over.

We need to make one slight modification to the movement before completing this one. The new movements came with a battery securing spring affixed at both ends. Clearly in a watch designed to allow battery exchange through a hatch, this part is redundant.

The final order of business is to grease and seat the outer case back gasket into the groove between the case ring and case sides and the inner gasket around in the inner surface of the case back.

Align the pheon symbol with the crown and press the case back into place with a satisfying click.

Simple, yet rather beautiful for something designed purely on its merits as a tool whose remit is simply to work reliably in a range of challenging environments. I’ll close this section with a profile shot of that superdome acrylic.

Next up, the younger of the two second gen Fatboys, a 1984 W10 watch, also fitted with a Marinium 947.111.

The movement on this one is much cleaner and its circuit lives. The problem is that its quartz crystal oscillator has been cannibalised.

This is a shame because I had thought initially that the working coil from the other watch and circuit from this one might make for a salvageable movement. And so this one too is consigned to the parts bin and we call upon the second of our two new eBay-sourced 947.111’s.

The hands on this watch are in better shape than on the older watch and although the dial is basically in excellent condition too, there is a slight smudge between the 11 and 12 markers (although nothing that ought to be visible to the eye in general use).

The view from the rear of this one with the movement installed is rather tidier than the first watch because the case has not suffered from a prolonged period caked in grot.

With both of these watches, I’ve tweaked the timing using the trimmer condenser, aided by the timing function on the Horotec Flashtest. The trimmer is extremely sensitive and barely perceptible adjustments can have quite dramatic effects on the timing.

The gasket installation proceeded as in the previous watch and we pause, having fitted the case back, to view the sprung centre-piece on the battery hatch rear surface, there to press the battery into position once installed.

And then there were two.

Third up, we have the oldest of the three watches and comfortably the one whose external facing condition suggests that it has lived the hardest life.

The crystal appears to have been partially melted, its surface warped and distorted. The hands around their bases show signs of corrosion but the dial itself looks very nice, set off by the lovely deep-toned tritium lume. The movement is an ESA 536.121 and it is this that marks this out as a first generation Fatboy, notwithstanding the later oval CWC logo on the dial.

The movement is a non-runner but both coil and circuit appear to have some life. Extracting the movement is straightforward, requiring nothing more than the removal of the stem followed by inversion of the case.

You should be able to see the extent of the corrosion affecting in particular the base of the minute hand. With the hands and dial removed, it was clear that the corrosion visible on the minute hand extended through to the hour and minute wheels, the two being fused together by rust. This would explain why the movement was a non-runner in spite of the fact that the electrical components appeared to be functioning.

With the two previous examples having been dispatched in such efficient fashion, my mood with this one veered away from a full movement service to make use, instead, of the already serviced 536.121 left over from my Hellas auto conversion project. In due course I will get around to servicing the CWC movement too but I just want to see this one up and running. Let’s get the dial and hands off and compare the outgoing movement (right, below) with its service replacement (left).

Interestingly, in contrast to the movements used in the later two watches, the CWC 536.121 (right) has had all of its calendar parts removed and the setting lever spring is profiled for just a single setting position, without the intermediate quickset position. We can see this more clearly with the setting levers from both movements removed and set side by side.

In the spirit of retaining the original functionality of the outgoing movement, I remove all of the calendar parts from my serviced movement and substitute the original setting lever spring.

Off stage, I had rather successfully removed pretty much all of the signs of corrosion from the hands and cleaned the case. With that done, the dial and hands could be refitted and I turn my attention to the choice of crystal.

Counter to the received wisdom that I appeared to have generated in completing three of the breed up to this point, my default choice of 31.7mm crystal proved too large for this first gen case. Instead I selected a standard profile 31.6 mm armoured acrylic paired with the original bead-blasted tension ring.

The stem on this watch was also quite badly corroded near the crown and needed careful cleaning. The gasket extracted without fuss and I selected the same replacement as used in the other two watches.

With that done, the movement and case can be united.

The different movement dimensions and case ring design mean that this watch uses just a single, rather substantial case back gasket.

The case back then presses into position, having first aligned a notch in its side with the crown position.

Battery and hatch fitted and we are done.

I’ve probably overused the Fatboy moniker throughout this post and so in the spirit of justifying its use with these earlier examples of the breed it might be worth comparing the profiles of the first and second generation CWC G10’s described here with a later slimmer cased variant from 1990.

Clearly the later watch propping up the two older watches is the slimmest of the three by some margin but the difference between the 1982 watch (middle) with the 1983 watch (upper) is not so obvious. Indeed with the higher dome crystal I’ve fitted to the second generation watch, the height from case back to the top of the dome is exactly the same at 13.67 mm. However, the high dome crystal is probably a millimeter or so taller than the standard domed crystal used with the first generation watch and so the charaterisation of the Marinium movement watches as medium fat is probably fair enough.

Let’s wrap this up with a shot of the three completed watches side by side.

This has been an enjoyable little diversion. I’ve learned a lot about the different variations on the CWC G10 theme and come to appreciate even more what fabulous little watches these are. In fact, now that I think about it, a revived G10 has to be just about the best value quality watch you can buy. Let’s review the main attributes:

  • A watch of genuine historical significance
  • A unique and distinctive case shape
  • Fabulously clear and simple dial layout
  • Tritium lume that ages beautifully
  • Domed acrylic crystal lending it additional warmth and character
  • Small enough to be as comfortable as you could hope for but large enough to assert itself.
  • Proven robust construction
  • A high-grade quartz movement with no calendar nonsense to detract from its credentials as a properly useful pick up and go wrist watch.

On top of all of that a dash of military provenance doesn’t do any harm if that is something that pushes your buttons.

I hope you all have a good winter holiday break and let’s hope that 2019 brings a great deal more positivity than 2018 (and 2017 and 2016). I’m quietly optimistic although possibly delusional.


*With apologies to John Cleese and Graham Chapman.