Tonnage IRL

[Fusek]

How did Kaleuns determine the tonnage of the ships they sunk in real life?

[Foghladh_mhara]

Lloyds Register. And add 10 %

[Sailor Steve]

Prior to the beginning of hostilities it was easy to obtain all kinds of information, especially on public shipping. Wartime ID books showed the GRT of each class of merchant, so they had a pretty good idea of what they were looking at.

[harzfeld]

Also I wonder how did Allied merchants knew where Allied's mines were? Didn't some Germans captured some merchants, boarded on ships, had access to bridges looking for maps or manuals revealing where British laid their mines at? It should go to intelligent report, useful information for kaleuns. It must be Bernard who was an administrator in department of counter-intelligence agency. I know escorts at ports usually carry that kind of information to lead other ships in/out of ports, but I am talking about mines laid across North Sea and English Channel.

[PhantomLord]

Originally Posted by harzfeld

Also I wonder how did Allied merchants knew where Allied's mines were? Didn't some Germans captured some merchants, boarded on ships, had access to bridges looking for maps or manuals revealing where British laid their mines at? It should go to intelligent report, useful information for kaleuns. It must be Bernard who was an administrator in department of counter-intelligence agency. I know escorts at ports usually carry that kind of information to lead other ships in/out of ports, but I am talking about mines laid across North Sea and English Channel.

Afaik no german u-boat commander ever was aboard a merchant. German Aux.-cruisers seized many ships but allied crews often had the time to destroy secret material. I don´t want to know how many bags with that stuff were marking the convoy routes...
Position of minefields were often captured via radio messages. The german B-Dienst (Beobachtungsdienst / naval intelligence) was very good in the first years.

[_Seth_]

Originally Posted by PhantomLord

Afaik no german u-boat commander ever was aboard a merchant. German Aux.-cruisers seized many ships but allied crews often had the time to destroy secret material. I don´t want to know how many bags with that stuff were marking the convoy routes...
Position of minefields were often captured via radio messages. The german B-Dienst (Beobachtungsdienst / naval intelligence) was very good in the first years.

I agree, i don't believe that any u-boat "commander" was ever aboard a merchant, but there were episodes where they examined vessels:


July 13. 1942, the Barents sea, the PQ 17 disaster:

The dutch merchant "Paulus Potter" is found abandoned by U 255 (Kaleun Reinhardt Reche, U-boat named "Der Fuchs"). Reche ordered some men aboard the abandoned vessel, and one of the men, the watch officer aboard "Der Fuchs", Hugo Deiring, found the secret codebooks together with a complete list containing the names of all ships sailing in convoy PQ 17.
Reche and his men concluded that "Paulus Potter" had been hit by an air-dropped torpedo, + a towing attempt had been made by the other allied ships before they choose to abandon her. Reche also noticed that "Paulus Potter" was heavily armed, with AA-guns, machineguns and a stern-mounted deck gun. Reche ordered the crew to load the last torpedo he had available, and fired it into "Paulus Potter". The merchant sank within 2 minutes after the impact.

Source: Knudsen, Sven Aage: "Ubåtkrig (U-boat war), Danor 2006


Edit: Addition from uboat.net: http://uboat.net/allies/merchants/1929.html

[Brag]

I you know ships you can guess the tonnage pretty close by kust looking at them.

[ToySoldier]

And as far I had read the listen to the emergency-calls of the sinking ships ... and by the name could they compare the Llyod-Register ...

[Fusek]

Interesting! thanks for the replies