you have a scene in your book where the U-Boat is attacking from the surface.
Why is that?
A German U-Boat wasn’t a submarine as we think of them today. U-Boat is the abbreviation of Unter See Boot or “under sea boat” that is, a boat which could go underwater for a limited time. The boats could not remained submerged for a long period of time. 24 hours was about all the men could take because the air became so foul and the CO 2 levels became unhealthy. The record is 63 hours, I think, and most of the crew had passed out from CO 2 poisoning.
While submerged, a U-Boat, running at full speed on its electric motors, could only make six knots. A submerged boat making that speed would run completely out of battery power in four hours. On the surface, however, running at full speed on its diesel motors, most U-Boats could make seventeen knots or better and could do so for days if they needed to.
Therefore attacking at night from the surface was the preferred method of attack. Boats would typically approach a convoy up moon, that is on the dark side of the convoy so the boat would not be silhouetted against the moon. This firing position was critical because a U-Boat on the surface at night was very difficult for convoy lookouts to spot unless illuminated against the moon.
In the first years of the war, when the great aces made their reputations, almost all of these attacks were made from the surface at night. By the summer of 1943, most Allied escort ships were equipped with radar which robbed the U-Boat of the advantages of making night attacks from the surface.
In this classic and often reproduced photograph, the U-Boat kommandant is supposedly making a submerged attack. The photo is posed, of course, and the man at the scope if Kapitanleutnant Kurt Diggins, who served as Captain Langsdorff’s flag lieutenant or personal orderly officer as the Germans called it, aboard the Admiral Graf Spee. Diggins escaped from Argentina, returned to Germany, and later received command of a U-458.
In the photograph, Diggins is actually in the control room of the boat looking through the sky periscope which kommandants used to search the sea and sky before surfacing. The attack periscope with its special ranging lenses and marks, used when the boat made a submerged attack, is actually in the conning tower just above Diggins. The space is so small it was impossible to get a picture of a U-Boat kommandant sitting at the attack periscope.
He did not excel as kommandant of U-458, sinking only two ships for a total of 8,000 tons before his boat was sunk on 22 August 1943. Most of the crew, including Diggins, escaped from the sinking U-Boat and were picked up by the Royal Navy and made prisoners of war. Diggins later served in the West German navy and only recently died, in 2007, at age 94.