WW2 German Timer, U-Jagd

I have been trying to find out how this German ww2 timer was used to “hunt submarines”. I do not own the timer, just very curious about the markings.

I’ve asked on a couple different military watch forums. I’ve received some useful feedback, but no one seems to really know, including the owner of the timer. It was apparently listed as a torpedo timer in some collecting book, but that probably is not correct.

Note the three tachymeter indices which are off by a factor of 2. Also, the units listed on the dial are sm, which would not be a rate. Annaherung apparently translates to “approximation”.

I’d be interested in hearing your opinion.

knight427

[Don Dahlberg]

I thought it was a torpedo watch, but I have changed my mind. I think it is a depth charge watch. See http://www.knirim.de/watchsto.pdf page 6.

This says both uses are correct: http://www.knirim.de/a0501mod.htm

I need to do some more reading.

Don
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[Hans Dahlke]

Here is my best take on the meanings (I am by no means an expert on German military watches but I do speak German).

Annaeherung means approach distance, i.e. distance to U-boat or ship to be attacked
m means meter and must refer to the depth of the U-boat
sm must mean Seemeile, the German word for nautical mile (not identical distances)
KM stands for Kriegs Marine, the name for the German navy
Oberkommando means headquarters or top command

Maybe this watch measures the time a sonar pulse travels through the water so that one can then estimate the distance to a ship. (I have no idea if they even had sonar in WWII).

My guesses seem to make sense if one considers that as the depth increases the pulse travel time increases (by a factor of two at twice the depth).

This must have been used on a submarine, as I cannot figure out how a surface ship could know the exact depth of an enemy submarine. But I am willing to stand corrected as I was only a child as WWII ended.

Hans

[burnz]

Going by what has been said so far---wouldn't it stand to reason that----if it were used on a u-boat--it would be for topedoes and if it were used on a surface vessel--it would be used for depth charges.
That make sense?

Thanks Hans and Don, I think we are getting somewhere. The info provided has spurred some new areas of research for me.

In the second Knirim link, it says the dial has a 1/100th minute scale. I had assumed the watch was a 100 second timer for some reason. I guess that doesn’t make much sense, and it certainly changes many of my deductions. I mentioned that the apparent tachymeter scales were off by a factor of 2. It appeared to me when looking at the 100m scale, after what I had incorrectly assumed was 100s (one full revolution), the reading was 2, as in 2 m/s when it should have been 1 m/s. This is of course wrong for too many reasons to list.

I still have a lot of details to look up and ponder, but one major issue is bothering me. If sm really is a distance (about 1.85 km according to Wikipedia) then the three indices don’t make sense. Distance should be proportional to time (increasing time indicates increasing distance). The scales on the indices are inversely proportional to time (increasing time indicates decreasing units) which of course would suggest these indices are tachymeters. So the units don’t seem to match.

Also, I was looking into the speed of sound in water. I believe the only useful number would be 1500 m/s. There are three main factors that change this number, salinity, temperature and depth. It looks like depth doesn’t control this equation until 1000m or more, which is beyond the operational depth of most subs. Also, any echo timing scale would be proportional to time (see Waltham ASDIC timer).



Finally, to address the comments by burnz. While your position is quite reasonable, it does not consider how the watch was used, specifically in relation to the indices. Torpedo timing certainly could have been accomplished with this watch as with most any other timer. The real question is, what function did the indices serve and how did the calculation work?

[burnz]

If any of the info ever comes to light---come back and enlighten us.
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[burnz]

It would be interesting to know the exact function, calculations etc.

Appears the formula is fairly complex.

[Don Dahlberg]

I was trying to figure out if the scales had something to do with sink rates of depth charges. Depth charges of different sizes have different sink rates. The sink rates seem to be from 2 to 4.5 m/s. You need to know these so that you know how far down as measured by time the depth charge has gone when it blew up.

I cannot figure how this would be used with this watch. You have a depth charge that has a sink rate of 3.4 m/s, do you pick the closest scale? What is the purpose of the blank area before these inner scales start counting down?

I really hope you find an answer.

I looked in Whitney's Military Timepieces and found nothing. We do have several German books on military timepieces at the NAWCC Library. They are in German, and my German is very rusty. We do have a former high school German teacher who volunteers. If you send a request to research@nawcc.org with your membership number, we might find something.

Don

[Clint Geller]

My guess is that the instrument was used to determine the distance of the source of a sonar echo from a surface ship. Sonar definitely existed in WWII, but I believe only surface ships ever were equipped with it. To my knowledge German subs, at least, never had sonar. (Subs didn't need sonar to find surface ships and WWII subs rarely if ever fought one another - that wasn't their mission. Both German and American WWII subs were intended primarily as commerce raiders. Furthermore, a submariner would give the enemy more information than he received if he resorted to an active sound reconnaisance system.) Hans' explanation of the factor of two is exactly right - it converts round trip transit times into approach distances. I have seen similar devices before.

I think there has been a breakthrough. I asked an owner of a U-Jagd to confirm if the dial measured 100 seconds or 60 seconds (marked in 1/100th minute). I was informed the watch hand makes one full revolution in 100 seconds, meaning one of my initial suspicions was correct.

With a little math, it can be shown that an object which travels 100m in 100 seconds is traveling at a rate of 1.94 seemeile/hr. That’s awfully close to 2, which is what would be displayed by the 100m tachymeter on the watch.

This makes more sense than assuming it measures m/s and is off by a factor of two. To say this has to do with the round trip timing of sonar seems logical until you try to actually work it out.

The round trip time of sonar is used to measure distance, not speed. I can’t conclusively say the indices are tachymeters, but I can definitively say they do not measure a distance. Distance is proportional to time; the indices are marked inversely proportional to time.

For anyone suspecting approach distance, that also does not work. Approach distance would decrease with time, but it would decrease linearly with time. This is clearly not the case here.

Finally, the distance units on a 100 second timer would have to reach 75 km at the 100 second mark (half the distance traveled by sound in water in 100s). FYI, that would be about 40 seemeile. The index in question is marked 2.

I’ve mostly convinced myself that the three concentric indices are tachymeters used to find the speed in sm/hr by measuring 100m, 150m, or 200m pace. Of course, that doesn’t make it true.