So it's near the end of the war and the Germans want to hit a specific target using jets. Using a couple of their XXI Type Uboats they devise a way to place a few navigational beacons in the Irish Sea for example. Would the British have to find it first or could they just jam it to defeat it? how long would it take to jam an unexpected signal? How big would the buoy/transmitter have to be? Thanks in advance.
I shouldn't have thought that the Germans would need to bother. A low-level attack using visual target acquisition would seem practical ; it would in any case have to be a suicide mission as the jets wouldn't have enough fuel to return to safety.
Well they sent escorts after German sub transmissions pretty quickly and by late war the escorts had HUFFDUFF equipment as well I believe. ASW aircraft may have as well. Uboats entering the Irish Sea to place transmitters looks pretty risky to me. Then there's the question of how accuratly they can place the transmitters as well.
HF/DF was targeted against U-boat communication frequencies, which might not be the same as navigational systems. However the British were well aware of German radio navigation going back to the "Battle of the Beams" in 1940-41, and I would guess that land-based installations continued searching for odd radio transmissions throughout the war. The principle is still valid, any transmission allows receivers to plot a fix, and a navigation beacon involves more continuous activation than just sending messages. Would there be some means of turning these autonomous beacons on and off for missions? Or would they be 'beaconing' the British continuously? A new buoy in a busy waterway might attract attention even if its function was not understood. Besides the transmitter, the beacon would need a power source, presumably batteries, and a substantial anchor to hold it place, plus cable or chain, so it might be a fairly substantial item for the deck force on a submarine to manage. Maybe the battery could be the anchor? If the whole thing could be made to fit into a torpedo tube, that might be the best way to deploy it. Precise navigation and placement by a submarine would still be a challenge. The smaller Type XXIII elctro-boote might also be a delivery option, several of them operated in British coastal waters in 1945.