Hi John,

Well after looking through several books I finally found this in Showell, Jak P. Mallmann. U-Boats Under the Swastika. Annapolis, MD: Naval Institute Press, 1987. ISBN: 0-87021-970-7. Copyright: Jak P. Mallmann Showell, 1987:

“The individual number of each boat, always prefixed by the letter “U” was usually allocated when the building plans were handed over to the shipyard. At this stage there could still be a considerable amount of work in planning the actual production process and in finishing design details, especially in the case of new projects. Keels were not laid until after a construction contract was issued…
.
.
To confuse the issue further still, a number of boats launched before the war were re-numbered for administrative purposes and therefore had two numbers. In addition to this the ship building yards also used a construction number which differed from the one prefixed by the “U”, but this hardly features outside construction yard documents.”

If I understand your last example Westwood says U69 through U72 were renumbered to U99 through U102. However all eight of these boats were ordered before the war and launched after the start of the war and they all existed at the same time until being sunk or scuttled during the war. Also U69 through U72 were all Type VIICs and U99 through U102 were all Type VIIBs. What’s more, U99 through U102 were all ordered on 15 Dec, 1937 before U69 through U72 which were ordered 30 May, 1938 (U69 & U70) and 25 Jan, 1939 (U71 & U72). This just couldn’t be more confusing.

The only conclusion I can think of is that this renumbering was a paper transaction only and it occurred before the boats were commissioned - there was never a commissioned U-boat that was renumbered but some were built under one number and commissioned under another. This would be consistent with Showell’s description of the renumbering being for administrative purposes. Of course that’s only a guess but so far I can’t find any records of two U-boats ever being commissioned with the same number. I would expect to find something like this mentioned in Rössler, Eberhard. The U-Boat - The evolution and technical history of German submarines. London: Arms & Armour Press, 1981. ISBN: 0-85368-115-5. Copyright: Lionel Leventhal Ltd, 1981 but I’m not having any luck – it’s a really big book (-: Also U-99 was a famous boat (commissioned and commanded by Otto Kretschmer) and you would expect having its ID changed along the line would be mentioned somewhere.

Perhaps someone else can shed some light on this.

Regards,

Ken Dunn