A 1934 tank with center seconds: pilot's watch, Longines medicus, or?

After an impulsive late-night eBay offer last month, this interesting little number arrived today - my second Longines and first ever tank. Since there doesn't seem to be much material here on this watch or its movement, I thought I'd share some research and questions.


Here's what I'm pretty sure about:

- A deco-style tank watch with single-step stainless steel case
- Serial number 5,320,4xx suggests production in 1934
- 9.40 movement with côtes de Genève finishing and center seconds complication. Runs well and winds and sets smoothly but shows its age. Seller claims it was "serviced" but it is adjusted well only in the crown-up position, and the regulator arm is as far to slow as it can go.
- Two-tone metallic dial appears to be original and has a lot of life experience 😁
- Blued hands appear to be original: very cute, plump, and stubby
- Crystal fits fine, but is not correct as its tapered sides obscure part of the 10 and 8 on the dial
- Crown appears to be original, or at least is the right shape.

Here's what I think I know but would enjoy your input:

Movement
The 9.40 movement appears to be seldom seen. Even Ranfft doesn't list it! According to this site, the 9.40 is an savonette produced between 1926 and 1939. It's an old-fashioned design - the multiple curving bridges on the train are a design approach carried over from late 19th century pocketwatches. The 9.40 is 9 lignes or 22.6mm in diameter – it is identical to the 10.40 except for its size and in fact shares all parts except for the main plates. (In this iteration of the Longines numbering system, the first number must refer to the size in lignes.)

The 1929 French catalogue shared by @bigbug1964 seems to show the 9.40 mostly used in ladies’ movements. I get the sense that this style of movement was a little bit old-fashioned by the mid-1930s.

Reference
I think this watch is a Ref. 3640, which is listed in the 1936 and 1937 French catalogs (but not the 1938 Italian catalogue). As seen in the image below, in 1936 the 3640 has the same hands, case, and dial as mine, but with dots rather than lines at the odd-numbers instead of lines. It's noticeable in the 1936 catalogue that the men's references all use the 25.17, except for the 3640. In the 1937 catalogue, however, Longines switched to the rectangular 25.17 movement for this reference. Perhaps it took them a while to adapt the 25.17 to the center seconds complication. It is interesting that the reference number was rooted in the style rather than the mechanicals - it is hard to imagine a brand today switching the movement type without changing the model number. 650Fr was about $43 US dollars in 1934, which would be about $940 today. Not an inexpensive watch!


The other examples of ref. 3640 that I can find all have ref 25.17, such as this nice one in 9k gold, currently for sale here on the forum. (I am not sure about the hands however.)


Doctor's watch or pilot watch?
What drew me to this watch was the center seconds complication, which recalls the Omega Medicus CK651, and the Rolex ref 2149 (the latter with quite a similar dial design). Member @imfagent449 suggests that the ref. 3640 was a pilot’s watch, and links to a Romanian site showing a number of examples of its use in Romanian military aviation during WWII (though none quite matching my watch). A doctor’s watch, a pilot watch, or both? I am curious why the Omega Medicus is widely collected while the Longines analog is little-known.




I've sent a request for an extract to Longines and will update the thread when it comes back. Your thoughts welcome in the meantime!

Neat watch, especially with the caliber 9.40. Thanks for sharing photos and your research.

I suppose that whether or not the watch should be considered a "pilot's watch" or a "doctor's watch" depends on how you define those terms. Some might say that any watch that was used by a pilot is a "pilot's watch", while others might say that the watch must have been specifically designed for pilots. To me, these center-seconds watches from the mid-1930s are intriguing, irrespective of what category they fall in.

Looking at the dial of your watch, I am not certain that it is original. To me, the hour markers look somewhat crude (both the execution of the numbers and the fact that the odd numbers are dots). The font of the sans-serif signature is also surprising, to me. There are original dials with sans-serif signatures from this period but the fonts that I have seen look different. Additionally, the dial foot appears to be white rather than the more typical copper tone. Below are examples of similar watches, though I believe that all of these have the cal. 25.17 rather than the cal. 9.40.

It would be great to hear from @Syrte as she has a lovely example of one of these (cal. 25.17).

Source: old eBay listing


Source: http://www.ceasuripentruromania.ro/ceasuri.php?id_article=98&language=english


Source: http://www.ceasuripentruromania.ro/ceasuri.php?id_article=98&language=english


Source: https://www.watchuseek.com/media/longines-25-17-dietrich-bale.4484738/


Source: https://www.instagram.com/p/CFNOnjBnZRC/


Source: http://www.ceasuripentruromania.ro/ceasuri.php?id_article=98&language=english


Source: https://www.catawiki.com/en/l/27001...utm_content=Barnebys&utm_campaign=Watches-COM

Source: https://zrhbrg.ch/products/longines-tank-art-deco

Source: https://www.instagram.com/p/CP_O9rKLO0F/

Very nice watch and great assessment, @joeshoup

I received an extract from Ms. Develey at Longines last week. I am shocked how fast they replied! I do historical research professionally and I have had very, very few archives in any country reply to me within a week, much less two working days. Kudos to them for staffing their archives properly, this level of service is encouraging me to focus more on Longines 👍

Unfortunately the abstract doesn't add a whole lot to the story:

Disappointing not to have a reference number, but the other facts match. I'm not surprised that it was sold to Canada, since the seller was in Toronto. The serial number suggests 1934, but there's no reason stock couldn't sit around for a year and a bit before being sold, so I'm not bothered by the invoice date.

Thank you for the reply, @DirtyDozen12. You may be right about the dial being refreshed at some point, as the open '6' appears to be very consistent across all the examples we've seen (both on the hours and the seconds track), whereas both are closed on my dial. I was aware of the controversy about the sans-serif fonts on Longines dials, so I entertained the possibility of a redial. However, the dial font on my watch does resemble the dials highlighted by @Syrte in this thread, and this tre tacche sold by Peter at VintageLongines.com:



More interesting is that this sans serif font is similar to that engraved on movements from the 1920s onward, to give a random example from a pocketwatch with a 3.8 million serial:



Just food for thought. I'm happy to accept that mine may have an old redial, but I'm not sure the issue of the sans-serif dial font in the 1930s is quite settled yet!

Regardless I'm having fun with this one despite all the scratches 😲

Thanks for the update.

Based on extracts that I have seen, an invoice date of 1936 would be expected with a serial number in the 5.3 million range. It is intriguing that a reference number was not mentioned, though. Maybe something to explore further.

To clarify, there are certainly original Longines dials with sans-serif signatures from the mid-1930s. However, they are not normally of the type that resembles the signature on your watch. Below is a photo that I took of one such example. The ones with signatures that resemble yours are usually from the 1940s.

Regarding the dial on Peter's Longines, I have doubts about its originality. The sub-dial has a highly atypical (read: incorrect) font/design. The sub-dial printing also appears to be misaligned.

I would advise against comparing fonts on movements with fonts on dials. After looking at many of both, I have not observed a meaningful correlation.

Adding another example for posterity.

Source: https://www.instagram.com/p/Cj5twW6ritF/

Thanks for sharing your experience! This is such a great crowd to learn from.

Adding this photo as it shows the dial without the crystal. Also, 18'107 is quite an early order number.

How early? I'd be interested to know more about the case numbers in Longines of this period, if you can recommend a source.

Here you go! 😀 https://omegaforums.net/threads/longines-case-numbers-an-introduction.156798/

Did I just custom order a thread? 😎

Interesting read. I see what you mean about a low order number, if they begin at 18000!

You did! I have been meaning to write a thread on case numbers for a while. Your prompt tipped me over the edge.

Just checked my records, these are the order number ranges I've got:

5-digit order numbers: 18'087 to 23'711
4-digit order numbers: 1'009 to 3'610

I will add this information to the case numbers thread.