So how did a captain decide the tonnage of a sunken ship?

[AG124]

From what I've read, US tonnage estimates for sunken Japanese merchants in the Pacific were often wildly innacurate, usually being too high (possibly because US commanders were thinking in terms of Western merchants, whereas many Japanese merchants tended to be smaller than the Western norm, but I'm not sure).

In the Atlantic, as you noted, recognition manuals often provided identification of the ship sunk, and in many of the books I read, identification of a particular ship sunk in the Atlantic was quite often correct. However, you are correct in pointing out that in hurried actions and rough weather, identification was not always possible; I have always received the impression that identification during such incidents tended to be less precise and more inaccurate than normal (although I may be incorrect on that - I would myself be interested in hearing more on the subject).

As well, remember that although belligerant merchants ships maintained radio silence under regular conditions, once torpedoed, many that were still capable of operating their wireless sets sent out distress signals identifying themselves. Upon receiving the name of the vessel, U-Boat commanders or watch officers could check Lloyds or recognition manuals to find the ship's exact tonnage.

Hope this helps a bit.

[Dietrich]

If the "class" of ship was identified, then the "tonnage" was indeed a precise number. It is the registered cargo capacity of the ship. For some ships (such as the Liberty cargo ship), the registered tonnage was fixed and that type of ship was mass produced and easily recognised. However, there were certainly small and odd ships that would not have been identified, or for which exact recognition would be nigh impossible.

Oh... and just as a reminder... "tonnage" is a volume, not a weight nor a mass. Ref: http://en.wikipedia.org/wiki/Tonnage

[Sailor Steve]

Originally Posted by Dietrich

If the "class" of ship was identified, then the "tonnage" was indeed a precise number. It is the registered cargo capacity of the ship.

Exactly so. Ships could be identified from the ID books available. I actually copied this note from a cargo ship I was researching:

Empire Explorer: Converted from liner Inanda. What did it look like? U-boat captain who sank her reported sinking Inanda, which means that A) his ID book contained precise information, and B) the ship still looked enough like her old self to be recognizable. Details - 75 survivors were rescued by a single MTB.

For some ships (such as the Liberty cargo ship), the registered tonnage was fixed and that type of ship was mass produced and easily recognised.

Actually that's not quite true. The GRT (Gross Registered Tonnage) was actually the number registered with the insurance company, and indeed it never changed. However, even the mass-produced Liberties varied a lot, and I'm still not sure why. American Liberties ranged from 7176 tons all the way up to 7240, and the British ones went from 7219 to 7255. That said, they were confined to a few specific numbers within those ranges, and were not random.

One other thing to remember is that a lot of reported tonnages were indeed wrong. The exact tonnages we get in the game should probably be considered the number arrived at after BdU confirmed the sinking via records obtained before the war, or the number confirmed after the war. Unfortunately, as with 'Weapons Officer Assistance', the numbers are probably a lot more precise than what they knew at the time.

[deepboat]

Originally Posted by AG124

From what I've read, US tonnage estimates for sunken Japanese merchants in the Pacific were often wildly innacurate, usually being too high (possibly because US commanders were thinking in terms of Western merchants, whereas many Japanese merchants tended to be smaller than the Western norm, but I'm not sure).

In the Atlantic, as you noted, recognition manuals often provided identification of the ship sunk, and in many of the books I read, identification of a particular ship sunk in the Atlantic was quite often correct. However, you are correct in pointing out that in hurried actions and rough weather, identification was not always possible; I have always received the impression that identification during such incidents tended to be less precise and more inaccurate than normal (although I may be incorrect on that - I would myself be interested in hearing more on the subject).

As well, remember that although belligerant merchants ships maintained radio silence under regular conditions, once torpedoed, many that were still capable of operating their wireless sets sent out distress signals identifying themselves. Upon receiving the name of the vessel, U-Boat commanders or watch officers could check Lloyds or recognition manuals to find the ship's exact tonnage.

Hope this helps a bit.

A while ago I copied some pages from 34thflotilla.com of some ship regognition profiles. Some warships and merchants. I found this handy to look at as some times there wasn't enough time to call up the manual when the scope was up and I was surrounded by targets. Is there a pdf file somewhere that I can download which has more ship's profiles and tonnages as the link the 34flottilla.com doesn't seem to work.

[Erich dem Roten]

Thanks for all the replies, I figured if the submariners knew the name of the vessel they sank then an appropriate figure could be easily obtained. I guess what bugs me is when an attack is made under duress, where a positive identification is impossible and the sub immediately (or shortly thereafter) submerges and begins evasion maneuvers yet often reports a "solid" number in terms of tonnage sunk. I would expect the majority of the reports to be estimations that ended evenly (10,500, etc.) rather than the precise numbers I've seen on places like uboat.net. Everyone brings up very valid points though; I just enjoy the discussion.

[Klaus_Doldinger]

Just one more question about ship identification, concerning nationality:I suppose that the recognition books included the nationality of the ship, i.e., you didn´t need to observe the flag to determine if your potential target was belligerent or neutral. In fact, this is simply impossible in the game most times at night or at great distances. Am I right?

[Ping Panther]

I had read a very detailed book from a Pacific fleet submariner a while ago that indicated that it was very common to surface right after a merchant sinking. Primarily, this surface contact was made for establishing a very accurate ship-kill report while on patrol. The sub captain would verify tonnage, cargo, and in particular the ship name/I.D, route from port-to-port info., etc. The author indicated that most of the estimates of sub captains of ship tonnages that were not checked on at sea, were often greatly exaggerated in the initial sub patrol records. Usually, many post-war verifications of war-time shipping logistics records from merchant ship home port offices uncovered many of these inflated battle statistics.