[Mush Martin]

Originally Posted by Puster Bill

Well, I used to be in the Signals Intelligence business (Ex-US Army 05H, Electronic Warfare Signals Intelligence Morse Interceptor), and I can tell you that while HF/DF would have been valuable in an immediate tactical sense, it wouldn't have been of lesser utility for future planning. Allow me to explain..

Direction finding can only tell you, within a certain margin of error, where a target is located at the moment you DF them. At close range, such as with HF/DF sets mounted on ships, this isn't as much of an issue. In a convoy situation, if you have a couple of ships that have DF gear, you can pretty much nail the location of the u-boat transmitting (provided, of course, that you know the relative positions of the two receiving ships with reasonable accuracy!). Even if you only have one ship equipped with HF/DF, you will still get a 'line of bearing' to the target, that you can run down.

At larger distances, say from the US and the UK to the middle of the Atlantic, the irreduceable errors inherent in HF/DF, caused by the action of the ionosphere, make finding a particular boat a matter of chance. At those ranges, a circle of 50 miles would be a very good error, with 75 or more probably the average result. You also run into another problem: HF/DF in a 'strategic' (ie., fixed land stations) sense, even when combined with traffic analysis and radio fingerprinting techniques, has little to no predictive value. In other words, unless you have assets within range to prosecute the contact when you DF them, you don't know if they are going to head North, South, East, West, or stay in that same spot, which makes targeting them with a Hunter/Killer group problematic. It can still be done, but it isn't anywhere near as efficient as cryptanalytical results.

Cryptanalysis has predictive value. If you can successfully read the messages you are intercepting, many if not most of the time you know what that u-boat is going to do in 24 to 48 hours in the future, or more. You know where he is going to be, so you can place assets like planes and Hunter/Killer groups in the area to meet them.
This allows you to free up some escorts from convoy duty to actually kill the u-boats before they come in contact with the convoy. That keeps the merchant losses down (because a boat in contact with a convoy could still get lucky, but a boat sunk before it even gets anywhere near a convoy has no chance). You can't use them effectively though if you don't know where the u-boats are going to be ahead of time, which really is only possible if you can actually read the traffic between BdU and the boats.

That was a large part of the OIC experience they had to convince the
admiralty that not only could they use it to review historical situations
for insight as the germans predicted they would be able to do. they
also had to convince them that the submarine tracking room could
forecast future movements of individual uboats and raiders based
on established patterns of normal behaviour and precedented patterns
of deviant behaviour. they were lucky to have Roger winn as there
First attempt analyst an intelligent and insightful man he was indeed
able to well predict a better than average percentage of movements
and patterns and showed an uncanny insight for being able to
pull together unrelated threads into a firm prediction of future
action, more importantly with the precedent and patterns established
So also were his succesors able to also.

the OIC predicted the channel dash two weeks or so prior to it
happening based the decrypts and traffic patterns and movements
of Kriegsmarine units such as destroyers and minesweepers
(each of which used totally different cyphers)
as well as Photo Reconassaince and traffic from OKM.
Sadly "A series of unfortunate events" including two seperate
photo reconnasaince flights in different areas that missed seing
the sortie due to mechanical failure, allowed the german units
to gain an early leadoff and they managed to maintain the
initiative through the voyage where inertia ruled the day
for the coastal and air forces.
M