Hi
Both the attempted Biber action against the "Archangelsk" and U 864's mercury mission have been referred to as "Operation Caesar". Regarding the Biber mission, there is one good word covering it: Confusion.

Regarding the Biber mission, Many sources say that the three U-boats involved were U 295/Wieboldt, U 716/Dunkelberg and U 739/Mangold.

I have also seen one article where there was a “?” put after U 739.

In the web page [www.wlb-stuttgart.de], one could for a while read U 295 U 318 (Will) and U 716. I wrote to professor Rohwer in March 2007 and asked about this, and he stated that U 318 must have been listed there by an error. He further wrote that as written in his books (Chronology of the sea at war) and listed by Wynn, the correct boats were U 295, U 716 and U 739. Then he removed U 318 from the web page.
However, now it's back again.

My friend Svein Aage Knudsen (author of Deutsche U-boote vor Norwegen) tells me that a letter from Reinhard Reche that can be found in the U-boot Archive in Cuxhaven states that U 739 didn't participate, but U 318 did. However in a written summary of the story that a Friend of Reche had sent to the commander of U 992, Hans falke, one can read that U 992 participated instead of U 739 (or U 318). Falke sent this summary to me.

Here is what I have written in my story of U 992 (not yet published on the net).

"In the beginning of January a daring raid was attempted. This story has been a bit obscured because of missing documentation (and by secrecy perhaps?), and several versions circulate today. (For example, Professor Rohwer mentions U 318/Will instead of U 992).
However, according to a written story Falke sent me earlier the three U-boats that participated were U 992, U 716/Dunkelberg and U 295/Wieboldt.
Two one-man U-boats (“Bibers”) with two torpedoes each had been attached to the casing of each u-boat, and were to be transported to the Kola bay to attack the large Soviet battleship Archangelsk.
The action failed however. With the low pressure resistance of the “Bibers”, the U-boats weren’t able to dive deeper than to periscope depth. When they tried to dive with the “Bibers” attached, the buoyancy of the “Bibers” ruined the suspension of their torpedoes, and the plexiglass domes cracked because of the water pressure.
The three U-boats with the “Bibers” returned to Norway on the 8th of January 1945."

About the three boats listed above, I asked Mr. Falke if this version was the right one, and he replied that "this account is very close to the truth". He also wrote that hes was quite sure that U 739/Mangold didn't participate. He also wrote he couldn't remember the name "Caesar", but that it could have been used by the Marinestab Nordmeers in the beginning.

I asked for more details later, and in a letter dated November 2. 2007 Mr. Falke wrote to me:
"Und noch einmal auf den "Biber" zurückzukommen, - Ich denke das das ganze Unternehmen ein improvizierten versuch war. Erfolgreich hätte es nur sein können wenn die U-Boote speziell dafür konstruiert wären. Aber dazu reichte die seit nicht mehr."
Which translates into something like: To return to the "Biber" once more, - I think that the whole operation was an improvised attempt. It could only have succeded if the U-boats had been specially constructed for this purpose. But there was not time enough to do that.

One more thing: A while ago a statement appeared in a book errata listing here on U-boat.net (Stern: Type VII U-boats), stating that U 992 had participated. I have reason to believe that this was written by a relative of one of the crew members of U 992, but I have not been able to confirm this.

This is how far I have come by this time.
After my correspondance whith Mr. Hans Falke who has been very kind and cooperative, (no offense meant to Mr. Rohwer or Mr. Knudsen) I tend to believe U 295, U 992 and U 716 were the three boats that participated in the mission.

Best regards
Vidar