The COSD is one of the rarer of military Longines, one of the better looking watches of its time, it has personality and a very distinctive and contemporary “tuna-can” design, a large crown and oversized fixed bars between the lugs.

And yet the factual information available on this watch is quite scarce, often contradictory and inconclusive.

It is not even clear how many COSD watches have been made, how many model-variants exist, who they were issued to, and if they have actually seen any combat.

It is not even exactly established what COSD stands for:

Company Ordnance Supply Depot

or

Command Operations Stores Depot ?

more on this later

So to get as many facts about this watch straight I started taking the watch apart to reverse-engineer it, and see what can be learnt from this.

The COSD watch used is Reference 2340, the case is made of brass and then heavily nickel-plated, it bears the serial number 2160, the statutory Broadarrow marking of British issued military timepieces as well as the C.O.S.D. Marking.

The back is also brass, an unusual construction solution, as usually brass-cased watches have stainless-steel backs. This one it is quite hefty and the finish grade, particularly on the inside is quite rough, but this only concerns the looks. The watch is infact very well built and all the parts are accurately fitted, the back screws in effortlessly and closes tightly

Some measurements:

Case Diameneter:  35.6 mm

case length, lug to lug: 46 mm

crown: 7.28 mm

lugs width: 18.3 mm

Inside, the case is accurately threaded, and there is a threaded brass ring with four notches. This ring screws down smoothly and the plexy glass, has a “talon”, it has an edge which is sandwiched tight between the upper case and the inner ring.

A similar ring is also found on many of the same-period “dirty dozen” watches

It is possible that here was a flat rubber gasket to help make the watch water-resistant. The rings screws in and out smoothly and there is enough space to accommodate for a gasket.

The movement is a classic Longines cal. 12.68N with center sweep-seconds. It is an early generation movement with no shock-proof device on the balance-wheel, the serial number is 6.9 milion and by the Longines factory records:

Originally, the serial number 6’900’xxx identifies a Longines mechanical manually wound movement, caliber 12.68N. It was invoiced on 2 May 1945 to the company Baume and Co, which was at that time our agent for UK.
 
The other parts of the watch were produced locally under license from Longines. Unfortunately, since the relevant archives are not in our possession, we are unable to provide any further information on your model.

The movement is firmly held in place by two flanges screwed to the movement and connecting to the inner case thereading.

On many COSD there is a distinctive shark-toothed movement holder, so either this has been lost and the flanges are a replacement, or the watch has been assembled this way, this will be difficult to tell for certain.

The crown is also made on nickeled brass, it is quite large, 7.28mm diameter, it is not threaded and on the inside it has enough head-space to accommodate a rubber gasket that would have helped to some kind of water-resistance

The dial is a flat one with the classical three feet, on the back it has the ZJ code for dialmaker Flukiger and the 1 code for Longines as well as its individual number.

On the front, the dial is classically printed, the original color should have been whitish, with black arabic numerals, a red 24 hours inner scale and the broad-arrow.

The indexes have no trace of there being – or there having been – any luminescent material.

The hands are quite distinctive, they are steel, the hour and minutes hand are similar to the ones found on other civilian tritium-dialed Longines, but these are slightly thinner and more pointed.

The center-sweep-seconds hand is very distinctive with a bevel-tail and a diamond-shaped point.

No luminescent material on these either

From these basic observation it seems that when designing this watch care was taken to insure some form of water-resistance, and this indicates its intended military use as a marine watch more than an airborne one.

A watch with no shock-proof is definitely not suitable to being used air-borne, where a superior resistance to hits, blows and dropping is mandatory – conversely, this feature is less of a must if the watch is meant to be used in water.

The idea that this watch is meant to be in some way shock-proof by the use of the jaw-tooth movement holder on a large case makes little sense, as when the back is screwed in the movement holder is pressed between the caseback and the movement and it does what its name implies, it holds the movement in place by pressing it down, and because of this, it has practically no elastcity.

The other flaw to this theory is evident when taking the watch apart. The dial edge fits snugly in the bevel on the inner case ring, so there is no flexibility there and in the event of a lateral blow the balance-wheel axis would easily snap broken

COSD, Meaning

It seems most likely that COSD stands for COMBINED OPERATIONS STORES DEPOT,

COMBINED OPERATIONS, have a website at this link:

http://www.combinedops.com

from their website:

“Combined Operations made a huge contribution to the successful outcome of the Second World War by planning, equipping and training for offensive amphibious operations after the evacuation at Dunkirk in June 1940. In the ensuing years, there were many raids and landings mostly against the Axis forces from Norway in the north to Madagascar in the south and from the Mediterranean in the west to the Far East, culminating in the D-Day Invasion on the beaches of Normandy on the 6th of June 1944.

The Command drew on the best practices and expertise the Royal Navy, the Army and the Royal Air Force had to offer to create a  unified force. Many of their top planners and experts formed the nucleus around which the Command was formed and, as the requirements of offensive operations took on an international dimension, the service personnel of many Allied countries proudly wore the Combined Operations badge”

And they have a now declassified manual on the web:

and on page 9:

This pretty much settles what COSD stands for

for the time being, any comments or input on this notes will be welcome