WW2 German Timer, U-Jagd

[knight427]

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



http://img.photobucket.com/albums/v717/bodenedelstahltx/uj.jpg
http://img.photobucket.com/albums/v717/bodenedelstahltx/UII.jpg
http://img.photobucket.com/albums/v717/bodenedelstahltx/U-jagd.jpg

[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

[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?

[knight427]

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).

http://www.collectorsworld.net/w57c.jpg

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.

[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.

[knight427]

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.

[Clint Geller]

I see your point about the nonlinear gradations on the inner tracks on the dial, Knight. But let's come at the problem from another angle. A timer can only measures time intervals. So then the question is: between what two events is the interval measured? The endpoint of the interval most likely marks some sonic event, such as the arrival of an echo from either a sonar pulse or an explosion.

A related question is: What piece of information would be so important that a special timing instrument would have been manufactured for it? Certainly, finding a submarine would have been important enough. Conversely, measuring the speed of a torpedo or a surface ship probably would not have been. (Besides, there were probably silent ways for a submariner to estimate the speed of an approaching surface ship without announcing to everyone in the vicinity that he was there.) As for meaasuring the speed of a submarine, that information is not very useful unless one can also locate him, and if you can locate him his speed is not that important. (When submerged, WWII subs ran on batteries and were very slow.) This leads me to the conclusion that the instrument probably helps a surface ship locate a submarine, as is also suggested by the link provided earlier on this thread.

So how can a time interval measurement help locate a submarine? Suppose there is a depth charge or "water bomb" involved in the method, as also suggested by the previously provided link. For simplicity, consider the case of a stationary ship. The surface ship probably has a good estimate of how far the depth charge was from the ship when it exploded. If the sound of the explosion subsequently reflects off of a submerged target and the echo is detected by the surface ship, that places the source of the echo somewhere on an ellipse whose two foci are the surface ship and the point of the explosion, and whose major and minor axes can be determined by the fact that the sum of the distances from any point on the ellipse to the two foci must be a constant. The value of this constant is equal to the total time elapsed between the explosion and the arrival of the echo at the ship, times the speed of sound in water. If now a second depth charge is exploded in a different location than the first, then the submarine is located at one of the two points of intersection of the two ellipses.

Now rather than listening for the sound of the depth charge explosion to reach the ship in order to start the timer (that might have been quite rough on the listening crewman's ears), they might have wished to start the timer when the depth charge was tossed into the air, building an appropriate time delay for the depth charge to reach its pre-designated detonation depth into the calculation. The time delay would have varied with the depth setting on the charge. WWII subs seldom dove much deeper than 200 meters, so settings of "100m," "150m," and "200m" would have made perfect sense.

For satisfactory results, this "triangulation" method would have required that the two explosions be a minimum distance apart. In fact, in order to interpret and use the results quickly and conveniently with an enemy sub in the area, it would likely have been advantageous to ensure that the two explosions were always the SAME distance apart irrespective of ship speed. (This would have facilitated reducing the procedure to one of using an easy, convenient look-up table of some sort.) Thus, for example, when your moving at 2 knots, you look at the instrument dial and it reminds you that you must wait 100 seconds between shooting successive depth charges set to detonate at 100 meters.

When one interprets the three inner tracks as prescribing a specific time delay, read off the outer track, for a specific ship speed, read off the appropriate inner track, each of the three curves appears to obey the equation:

delta(t) = [L(d) / V] - t(d)

where L = 200 sm for the outer curve labeled "100m,"
and L = 300 sm for the middle curve labeled "150m,"
and L = 400 sm for the inner curve labeled "200m,"
or in other words: L(d) = 2d nautical miles

t(d) can be read directly off the dial as: t(d) =6 + 0.07d seconds

15 knots would be a reasonable max surface ship speed for the procedure, since extraneous noise form the surface ship's own engines and motion might have become limiting above that speed. (WWII Subs could not move that fast, especially submerged.)

[Kent]

Here's my two cents worth of basic WWII naval information:

One of my minor hobbies is reading about WWII submarine and anti-submarine activities, albeit mostly about American submarines in the Pacific. Nevertheless, I've read some on Allied and Axis activities as well. Curiously, although there has been a lot written about U-boats in the Atlantic and Mediterranean published (in English) and a lot published about Allied anti-submarine warfare in those waters, I can't think of a single book published (in English) that discusses Germen anti-submarine warfare. Thus, anything I've written below is only based my knowledge of Allied equipment and practices, and German U-boat accounts.

American, British and German WWII submarines had active sound ranging equipment (ASDIC, SONAR, etc.) that emitted a sound pulse from a transducer. The axis of the transducer provided the bearing; the time of the return echo provided a close, but not exact, range. I believe this was displayed on a cathode ray tube. This was a fairly close range system and the return echoes would come too fast and be too numerous to use a stopwatch for the time interval. The point is moot because active sound ranging was hardly ever used by submarine captains due to the fact that it could be heard by the enemy, who could then determine the submarine's bearing.

Passive listening was almost universally used, with the pitch and beat of a ship's propellers indicating to the sound equipment operator the type of vessel and its speed (the bearing again comes from the axis of the listening transducer - the operator aligned the transducer to the point of greatest signal strength). The plotting of successive listening points over a few minutes gave a much better indication of the vessel's speed.

American, British, Japanese and German (and probably Italian) WWII anti-submarine ships used active sound ranging extensively. I think that 12 knots was around the practical limit beyond which the noise of the water moving around the sound transducer's housing would overwhelm the return echo. This was a major stumbling block in designing acoustic homing torpedoes. Again, I believe that the range was displayed on a cathode ray tube.

There was no measurement of depth of the submarine. Ships and subs had sound fathometers (same basic equipment as SONAR), but these were pointed straight downward. The SONAR or ASDIC was aimed at a fixed angle somewhat downward (probably no more than 30 degrees). This created a cone (again, aimed somewhat downward) from within which an echo could be received. Usually, when the depth of a suspected submarine was unknown, a first pass was made over the sub without dropping any depth charges. The range at which the return echo was lost (due to the sub being below the bottom edge of the cone) indicated the depth - AT THAT MOMENT. The ability to move in three dimensions was a key to the subs' evasive technique.

Oh yes, American WWII fleet subs topped out at about 9 knots underwater, but rarely moved that fast due to the high battery discharge rate. Other nations' submarines probably had similar capabilities. However, short bursts of high speed were used during evasion when the sound of exploding depth charges masked the noise of a sub running at high speed.

Nobody received any return sound of a depth charge explosion echoing off of a submarine. The noise and reverberation of a 500 or 650 pound depth charge exploding took many minutes to die down to a level at which useful sounds could be distinguished.

Accepting the above information, and recognizing that American, British and German ships had RADAR-controlled gun ranging and aiming systems in addition to older optical systems (which the Japanese developed to the ultimate) the question arises, what's left to use a stopwatch on?

The standard American submarine torpedo, the Mark-14 provided a choice of two range/speeds; 4,500 yards at 46 knots and 9,000 yards at 31.5 knots. The Japanese Long Lance torpedo was faster and went further. I believe that the German torpedoes were also superior to the Mark-14. I'm not sure if they had a choice of speeds. However, the Germans had also developed an electric torpedo (which left almost no wake). Electric torpedoes tended to run slower than steam torpedoes. A choice of speeds or type of torpedo (subs would sail with a combination of torpedoes aboard) could account for the different scales.

American WWII submarine practice was to try for a range of 900-1,200 yards for a shot. Firing a torpedo at a target over 2,000 yards was considered to be somewhat chancy. The Japanese probably took longer shots, but the torpedo's range was only part of the equation. Errors of target speed and angle on the bow (direction of travel) are magnified by distance. Also, the longer the shot, the longer the time period within which the target may change course (or speed). A zigzag course was standard submarine evasion practice.

None of this directly addresses the purpose of the watch, but hopefully, it will bring the discussion back down to earth.

[Kent]

Addendum:

In addition to explosive noise masking sound returns after a depth charge explosion, the movement of the water due to the explosion also distorted and masked echoes.

A ship dropping depth charges while moving at only one or two knots is likely to get its stern blown off.

[Clint Geller]

Hi Kent,

My understanding is that depth charges were not simply "dropped," but were flung into the air (whether mechanically or chemically, I'm not sure), specifically to get them away from the stern of the ship. I had assumed that this explained the first six seconds of the t(d) expression I gave previously.

Secondly, I rashly assume that the German militaria link given earlier in this thread has some basis in fact, even if we don't completely understand it. I quote from that source:

For example, the ‘U-Jagd’ (underwater hunt) stopwatch was customized to show approach in sm and depth in m. These stopwatches were used by surface vessels while using depth charges to hunt for submersibles.

If we can distinguish "submarine hunting" from submarine killing, this suggests that some kind of an explosion, perhaps one smaller than those associated with the kind of depth charge intended to kill a submarine, was used to determine the position of a sub. If not, then it's one hell of a coincidence that the equations I proposed based on that picture just happen to work. Even if I may have some details wrong, I would bet that the three interior lines of numbers on the instrument dial relate only to the outer track as a kind of "calculator" and do not relate to the position of the sweep hand. The equations work, which is no coincidence, whether my explanation of them is correct or not. Do you have a plausible alternative explanation for these equations?


By the way, when discussing sonar, what period of WWII were you thinking of? By the time the US entered the war (officially, that is), German surface ship operations were mostly over and done with. Thus I would assume that this "stopwatch" was constructed during the early part of the war prior to 1941, when sonar capabilities were far less widespread. Obviously, if surface ships had sonar then, they wouldn't have needed to find submarine using depth charges, and if we're talking about a point when surface ships didn't yet have sonar, I'm guessing subs didn't have it yet either. Similarly, I'm not sure surface ships would have had radar gun-ranging and aiming systems prior to 1941, either. Perhaps you know the relevant introduction dates for this technology. (Heck, for the first year and a half of our participation in the war, our subs didn't even have reliable torpedoes - of any speed.)

As for "short bursts of speed," I can tell you that the required shaft horsepower for a submerged submarine increases approximately as the third power of the ship speed. Thus to accelerate from 9 knots up to say 15 knots, would require an increase in power output of 463%. And even that's optimistic since it assumes the conversion efficiency of the screw doesn't decrease due to increased cavitation and turbulence. Thus, I suspect that a WWII sub's burst capability was fairly modest.

[knight427]

Hi Clint,

Thanks for the great post. I agree with the vast majority of what you said. There are a few areas up for discussion however. (this is fun)

…if you can locate him his speed is not that important. (When submerged, WWII subs ran on batteries and were very slow.)

This is not necessarily true. From what I have read about submarine hunting in WWII, the submarine’s course was very important to know. Due to limitation of sonar, as the attacking ship neared the submarine, it would lose contact about 300m out. The attacker would then need to lead the sub for this distance plus the sinking time of the depth charges. It’s my understanding that the Allies developed better weapons than depth charges through the war (see Hedgehog link below), but I have not seen anything to indicate the Germans had a comparable system. Take a look at the link for a better explanation of how the British used ASDIC (their SONAR).

http://www.uboat.net/allies/technical/asdic.htm
[scroll down to “The Attack”]

The gist of all this is that it was critically important for the attacker to know a subs location, speed and heading to mount an effective attack. Submarines were well aware of the “blind time” prior to attack and used that time to take evasive action. I believe I remember reading that depth charge attacks had only a 7% success rate.

So how can a time interval measurement help locate a submarine? Suppose there is a depth charge or "water bomb" involved in the method, as also suggested by the previously provided link. Etc…

I like it. The geometry involved is quite interesting. However, I believe there is a fatal flaw with this creative method. When a depth charge detonates, it creates a lot of noise and also significantly disturbs the water. I have read that it can take up to 15 min after a depth charge attack before sonar becomes effective.

http://en.wikipedia.org/wiki/Hedgehog_%28weapon%29
[read the 1st advantage of the Hedgehog weapon system]

[knight427]

I see in the time it took me to get my references together, Kent posted basically the same info and seems to speak with a much greater degree of authority on the subject.

Clint, I like the idea that perhaps the indices were actually a sort of reference table independent of the time keeping.

[Kent]

... I'm not sure surface ships would have had radar gun-ranging and aiming systems prior to 1941, either. Perhaps you know the relevant introduction dates for this technology. ...

Clint:

The Bismark had gun control radar. She was sunk in May, 1941.

More later,

[Clint Geller]

Kent,

OK, but the Bismark was Germany's newest and greatest ship, sunk on her maiden voyage. If any ships in the German navy were going to have radar, they would have been the Bismark and her sister ship, the Tirpitz. Conversely, the US battleships sunk at Pearl Harbor had radar gunnery control added only after they were refloated.

Knight,

I take your point about knowledge of a sub's speed being important after all. But without sonar I don't see how this information would have been obtained; and with sonar, I don't see any reason for the instrument we're discussing???.

[knight427]

Clint,

I believe the watch may have been used in conjunction with sonar, but certainly not to time echoes. My best guess at this time is that perhaps a sub’s position was tracked on the sonar screen (Kent suggests that the soanr output the location on a CRT screen). I assume that the observing ship could be sitting still and could use the sonar screen to time the pace of the sub across 100m, 150m and 200m. I guess this info would have to passed along the attacking ship.

Then again, if the attacking ship was the one using sonar with the watch in this manner, the output would be the rate of gain on the sub.

One thing that still bugs me about my own theory is that the units on the supposed tachymeter are a distance, not a rate. The “per hour” could have been assumed, but the limited documentation on this watch mentions that it was used to find Approach and Depth. So the units are consistent with Approach, but the Approach would decrease linearly as I mentioned previously. So I guess there is a conflict either way.

Note that if the units are indeed Approach, then there must be some speed dependent coefficient of deceleration built into it, like water resistance. But this would suggest a non-powered drift. That doesn’t make any sense at all. Also, if you extrapolate the index out, the Approach would reach zero at a time of infinity.

Out of curiosity, does anyone know the years of service for the Admiralty Pattern 6 timer pictured way above? My updated theory now depends on the German sonar ability to plot position automatically. The British timer used with ASDIC suggests that ASDIC was incapable of automatically plotting position (at that time).

[Don Dahlberg]

It seems to me you have it now.

You follow an object over a 200m course. Say it takes 40 seconds. Using the Blue 200 m scale, you get a speed of 10 sm/hr. That is 0.200 km in 40 seconds or 18 km/hr. You gave us 1.85 km/sm, so divide 18 km/hr by 1.85 km/sm and you have a speed of 9.7 sm/hr, which is close to 10.

If you follow the ship for 100 m, then you use the yellow dial. At 10 sm/hr, it would only take half as long or about 20 seconds. At 20 seconds you would read about 10 sm/hr on the yellow dial.

The non-linear scale is due to the fact that speed is inversely related to time for a given distance.

The scales stop at 15 sm/hr as the fastest speed they need to measure. They could have added higher speeds for fewer seconds, but they would get ever closer. For 100 meter course, 1 second would correspond to 195 sm/hr.

So it is a way to measure speed without having to do the math, which is what a tachymeter is ( Greek: Takhus means speed and Metron distance). Whitney's Military Timepieces discusses Tachometers on page 268ff. It only shows watches designed for 1 mile base, but says they may be designed for 1/4/, 1/2 miles or 100, 200 or 300 meter bases.


Don

[Konrad Knirim]

Hallo friends,
here is the description of use for the U-Jagd, sorry in German, I hadnt time to find an adequate translation, maybe someone can do that. It is really a 100 sec timer, saying that it runs 100 sec for one turn!
. Gruesse/Regards/Salute K o n r a d K n i r i m
. konrad.knirim@t-online.de
. http://www.knirim.de

'Die U-Jagdstoppuhr ist eine Stoppuhr zur Ermittlung der
Annäherungsgeschwindigkeit. Das Zifferblatt trägt am äußeren Rande eine Einteilung in schwarzer Farbe von 1 – 100 sec, was der Zeit für eine Zeigerumdrehung entspricht. Nach der Mitte zu sind in den Farben grün, rot und blau drei Kreise für Entfernungsabnahmen von 100 m, 150 m und 200 m angebracht, die nach Seemeilen eingeteilt sind. Die U-Jagdstoppuhr wird bei einer beliebigen E-Messung des S-Gerätes in Gang gesetzt. Sobald diese Entfernung um 100 m oder 150 m oder 200 m abgenommen hat, wird die Uhr gestoppt und auf der betreffenden Skala unmittelbar die Annäherungsgeschwindigkeit in sm/Std. abgelesen. Das Ablesen von Mittelwerten ist ohne weiteres möglich. Die Annäherungsgeschwindigkeit ergibt unter Berücksichtigung der eigenen Fahrt die U-Bootsgeschwindigkeit. Ist die Annäherungsgeschwindigkeit höher als die eigene Fahrt, so läuft das U-Boot mit der Differenz auf Gegenkurs; ist sie kleiner als die eigene Fahrt, so läuft das U-Boot mit der Differenz auf gleichem Kurs. Hierbei sind die Begriffe "Gegenkurs! und "gleicher Kurs" nicht wörtlich zu nehmen, sondern nur als Annäherungsrichtungen zu werten.'



[b]

[knight427]

Thanks Konrad! I don’t know any German, but I can copy/paste into a translator.

AltaVista Babel Fish Translation:
The antisubmarine chase stop watch is a stop watch for the determination of the approach velocity. The dial carries an organization in black color of 1 - 100 second, which corresponds to the time for a pointer revolution at the outside edge. After the center too blue three circles for distance acceptance are by 100 m, 150 m and 200 m attached in the colors green, red and, which are divided according to nautical miles. The antisubmarine chase stop watch is started with any e-measurement of the s-equipment. As soon as this distance decreased by 100 m or 150 m or 200 m, the clock is stopped and read off directly on the scale concerned the approach velocity in sm/Std.. Reading off from average values is easily possible. The approach velocity results in the submarine speed with consideration of the own travel. If the approach velocity is higher than the own travel, then the submarine with the difference runs on reciprocal heading; if it is smaller than the own travel, then the submarine with the difference on same course runs. Here the terms are "reciprocal heading! to take and "same course" not literally to rate but only as directions of approach.

I’ve never seen such a clear translation in Babel Fish.

The watch was used to calculate approach speed in sm/hr. The only question now is how to interpret the method of observation.

[Norman Bliss]

Looks pretty simple once the scales are explained. I take e-measurment to mean echo measurement (echo ranging) and s-equipment to mean sonar.

Start the watch when the sonar gives you a distance reading, and stop it when that reading is decreased by either 100meters, 150 meters, or 200 meters, and read the speed of approach from the appropriate scale. As the sub is submerged, if the chase vessel is heading toward the sub that distance will decrease as submerged subs couldn't move as fast underwater as surface vessels at speed (what a difference between then & now, when subs move faster underwater than on the surface).

The speed of approach is the combined speed of your vessel (the chase vessel) and the submarine. If the indicated speed is greater than the speed of the chase vessel, the sub is on a reciprocal course (coming towards you-speeds combine). If the speed is less than the chase vessel, the sub is going away. The sub's speed is the difference between the indicated speed and the chase vessel's speed. One needs to adjust for the fact that the sub is probably not on exactly the same or reciprocal course of the chase vessel.

The choice of 100, 150 or 200 meter scales gives some leeway in taking a reading. If you miss the 100 m mark, you've still got the 150 & 200 m points, something that can happen if the approach speed is high. Quite possibly the chase vessel would start three watches and average the speeds shown.

Norman

[Hans Dahlke]

To all,

a most interesting discussion!

Regarding the dates mentioned in the various responses I wonder if the book shown beneath the box containing the watch provides any information. It shows a title starting with a capital "J" and possibly followed by an "a," the beginning of the word "Jagd?" Could this possibly be an instruction manual for this watch?

Furthermore, the shown date of Berlin 194x looks to me like 1940. x could only be one of four digits, and 0 (zero) seems to me the most likely for the small curved visible portion.

It would be nice to know the origin of this picture, and if, indeed, this is an instruction or similar reference manual how one could obtain such a manual.

Hans

[Norman Bliss]

I live in Groton CT and I stopped by the Submarine Force Museum today, but although it was open there wasn't anyone who could talk about the watch or sub chasing (there isn't even any info about anti-submarine warfare except when it talks about subs sunk in WWII).

There was an interesting watch, however. It was a Waltham pocket watch captured from a Japanese patrol boat off Manilla Harbor in 1942 by the US sub USS Salmon. Apparently it had been confiscated for Japanese use when they occupied the Phillipines.

click here (http://pages.cthome.net/nobliss/waltham.jpg)

Norman

[Clint Geller]

A little bit of Internet research I had time to do indicates that ASDIC, or radar was developed during WWI. Thus by WWII, I imagine it was pretty widespread. That being the case, it is unlikely that anyone would have used explosions to locate submarines during WWII, if ever.

[Kent]

... I assume that the observing ship could be sitting still ...

Well ......

....... No. Although there are accounts of destroyers (or other anti-submarine craft) lying quietly, listening passively, waiting for the submarine to make a noise by which it could be located, to do so invited a torpedo attack from the sub. Usually, a plot was started showing the relative positions of the sub and its (moving) hunter. The sub's course and speed could then be derived from the chart.

[Kent]

Hi Kent,

My understanding is that depth charges were not simply "dropped," but were flung into the air (whether mechanically or chemically, I'm not sure), specifically to get them away from the stern of the ship.

Well ....

.... somewhat. The real purpose was to drop a wider pattern of depth charges. Smaller anti-submarine craft had simple, tilted racks from which the depth charges would roll off of the stern.