This is a question about u-boat technology in WWII.

I am trying to reconcile an official account contained in the Ships Log of a US Navy destroyer escort at the National Archives in College Park, Md, and a story related to me by a member of the crew.

I am working on a theory as to how in the dark of night — it might be possible for a DE and u-boat to come into close contact before either became aware of the other.

If a sub was to surface close to a DE, it might be too close for the DE's radar to pick up. As I understand it, the radar transmits a signal, then the transmitter shuts off, and the receiver switches on so it can receive the returning signal. If the target is too close, the signal comes back immediately, too soon for it to be received. That may explain why the DE did not detect the sub until they were passing it at close range.

From the German side, the question is: How could it happen that a u-boat would not know the DE was there? I have a theory for discussion.

The situation was this:

A convoy of 20 merchant ships is to the North, steaming about 12 miles off the irish coast. It is escorted by 3 DEs and 1 Porter class destroyer. A fourth DE is to the South, investigating a submerged contact (probably a false one) and dropping depth charges. The DE is under orders to return to the convoy as soon as possible, because the Escort Commander and Convoy Commodore feel their 5 escorting warships is inadequate for the 20 merchant ships. The DE breaks off its attack and turns north. A u-boat is between it and the convoy.

(1) The u-boat captain could certainly hear the depth charges, and it may have given the him a false sense of security, believing the DE to the South was not a threat.

(2) The u-boat, still submerged, turns North while the officers worked out a plan to attack the convoy. Here is the first question — with the u-boat's screws turning at high RPMs, could they hear the screws of the DE coming up behind them? In other words, would their own noise have masked the sound of the approaching DE?

(3) The u-boat captain knew his only hope of catching a 14 knot convoy that was several miles to the North was to surface the boat and run on his diesels. They come to periscope depth, the captain takes a quick look around, and because of the darkness, fails to see the DE coming up behind him. Perhaps he is over-anxious, and in a rush to get after the convoy. Besides, he thinks the DE is still fooling around in the South with a false contact.

(4) The u-boat surfaces, and the captain comes up from below only to see the DE bearing down on him. He calls for an emergency dive, and everyone rushes to get the sub back under the surface, which explains why it did not fire on the DE. I would imagine in any case, that no sub wants a surface action with a better armed adversary, especially at close range.

(5) Aboard the DE, the Officer of the Deck on the flying bridge may have opted to hold his fire because he thought he was too close to depress his guns enough to hit the sub, and feared a strong retaliation from the u-boat. He could not know that the sub's deck guns were not manned.

(6) As soon as they had passed each other, the DE speeded up, came about and attacked, attempting to ram. The sub submerged and the DE fired Hedge Hogs. There were three explosions, and an oil slick appeared.

(7) The DE dropped a night marker on the slick and headed North in compliance to orders. They obtained permission to return and dropped a few depth charges on the spot, but did not have a sound contact. The crew felt sure they had sunk the u-boat, but for various reasons I think not.

Any reactions to this interesting and unofficial story? The official story contained in the ship's log is very sparse and makes no mention of anything on the surface.