Tonnage measuring

[hauptmannn]

I know in the Kriegsmarine u-boats and surface ships state the tonnage of the merchant ship sunk, i am wondering how they get this tonnage? How do they know the ship weighed this much? Do they use water displacement or something?

[Xavier]

usually, tonnage is measured by water displacement, and for record purposes, if ship type could not be identified, an aproximate was used.

regards

Xavier
Instandsetzungtruppfuhrer

[Mark V]

Warships are measured by their displacement, but merchant vessels aren't. They have totally different units of measurement - more practical and meaningfull to shipowners... (what they care what the ship weight ?? - it is the cargo capacity they are interested)

Merchant shipping tonnage is/was measured by:

- gross register tons
- net register tons
- deadweight tons

There is plenty of info available easily how they are measured exactly (differences between shipping authorities in different countries, different times), so i don't get into that swamp here...

German U-boats used gross register ton (GRT) to measure their victories. GRT has nothing to do with displacement of ship, as it is calculated from volume of enclosed spaces of ship with certain rules and exceptions.

And where Germans got those values ??

Many times, when target could not be distinguished properly - by estimate. But when circumstances allowed - by exact recognition of ships class and name - from published ship catalogues.


Regards, Mark V

[Andy H]

Hauptmann wrote:

I know in the Kriegsmarine u-boats and surface ships state the tonnage of the merchant ship sunk, i am wondering how they get this tonnage?

In addition to Mark V's answer, what you have to remember is that after the war many errors were found in the German records, many due to the estimates made at the time. With cross-referencing German & Allied records we now have quite accurate tonnage losses and how they related to individual U-Boats etc.

Some U-Boats found there wartime tonnage dramatically cut, since they over estimated, whilst others had there tonnages increased

Some U-Boat commanders received their Knights Crosses due to tonnage totals given at the time, and yet after this cross referencing many were found to be un-worthy so to speak of their Knights Cross etc

Andy H

[Erik E]

I have read quite a few books about Norwegian merchant ships in ww2, and many survivors says that oten the submarine would surface several hours after the attack to question the survivors for name, tonnage and cargo.
In many occations, the survivors were given water, rations and even direction to shore. In one occation, a Norwegian captain was severly wounded. The submarine brought him onboard and took him back to France. Unfortunately, he later died on a hospital in La Rochelle.

Erik E

[Roger Griffiths]

I remember a WWI film of a U-Boat on the surface after having sunk a British freighter. The Captain referred to his LLoyds register of British ships and crossing out the ship entry sunk.

Roger

[varjag]

Most of the time the tonnage estimation seems to have been one - made visually. Naturally it tended to err on the 'positive side'. As Andy correctly pointed out this resulted in erronous awards - and medals. The silhouettes of most merchantmen of that time were so strikingly similar, that I - for one have never understood how any kind of ID, least of all through a periscope, could carry any coin. No matter how many hundreds of pages of recognition manuals the U-boats might have carried as the merchantmen numbered in their thousands. Least since 'most recent modifications' - unknown to the Germans would have drastically changed the silouhettes of any ship.

[lijn34]

As far as I know, the German U-boatcrews often used prewar editions of the Lloyds Register of Shipping (as already mentioned by Roger Griffiths). This could of course only be done if the name of the ship (or perhaps only the class of ships, sisterships?) was known.
If not, they used their own estimate for the size of a ship; this was of course often exaggerated (perhaps on purpose for the commanders tally).

Greetings LIJN

[Erik E]

Another way I heard, was to listen to the "SOS" sent by the sinking target....

EE

[Christoph Awender]

Just an additional note. The ships which were torpedoed sent the letters "SSS" for submarine, submarine, submarine then the name and position. Most ships were identified by these calls, later news releases etc....

\Christoph

[Mark V]

Just an additional note. The ships which were torpedoed sent the letters "SSS" for submarine, submarine, submarine then the name and position. Most ships were identified by these calls, later news releases etc....

\Christoph

True.

Purpose was to ensure that even if radio transmission was cut very short (even just the SSS part) - by 20mm shells shredding the radio room or mast of an ship crashing to water (radio antennas with it) - there was still some valuable information available for naval intelligence.

- attacked by submarine
- time of attack
- rough location fix by radio direction finding stations

If ship could also transmit it's name and location - practically all the essential information had been sent, and hopefully heard...

British had also other letter codes that identified merchant raiders and enemy warships. There was good reason for such procedures - radiowaves are for all to hear, and especially German surface raiders were quick to react if their victim tried to send an distress message, returning by gunfire and jamming the radio-channel in seconds after transmission had started.

Regards, Mark V