At 22:00 hrs, nine German E-Boats left Cherbourg for Lyme Bay. They knew exactly where they were going to intercept an Allied convoy and as anticipated, encountered Allied destroyers protectively screening ships participating in Exercise "Tiger".
They launched a torpedo attack against one destroyer claiming it was sunk, but no record exists of any Allied warship being lost on that date.
Moving further into Lyme Bay the slow moving convoy T-4 was found and attacked with three ships claimed as sunk, the official Allied version only admits two LSTs sunk and a third damaged.
Because the E-Boats went directly to the convoy with no hint of searching for it, or encountering it by chance on a routine patrol, may suggest they had been "tipped off" through intelligence sources.
D-Day was only weeks ahead and Allied intelligence was keen to promote their deception plans and convince the Germans the invasion of Europe would take place at Calais. Double agents in England were feeding dis-information to Berlin to this end and to further increase their reliability could have passed genuine, true intelligence about Exercise "Tiger" to enhance their believability.
This is supported by activity and meetings at the very highest level suggesting the Germans were tipped off about Exercise Tiger. Admiral Moon took Captain Moran with him to London to confer with Rear Admiral Kirk and the British Admiral Bertram Ramsay. On their return the following day, whatever they discussed in London was passed on during a meeting with Admiral Hall aboard the USS “Ancon” where they were joined by Sir David Petrie. He had been personally appointed by Winston Churchill to reorganize the United Kingdom’s intelligence services, and was now in charge of the nation’s security. It is remarkable that he should leave London and join such high-ranking US Naval officers, and it can only be speculated as to why the security of the nation should be involved with a totally military operation organized by another Allied nation.
Similar but less grand exercises for American, Canadian and British forces had come and gone, none of which had attracted his attention. So there had to be a very good reason for his interest this time. Allied planning consortiums all operated under the same protective cloak of secrecy relating to personnel and locations, so Sir David could find no fault there. Only a handful of very senior commanders, and even fewer of their staff officers knew the details of the projected assault on Normandy. Code named “Bigots”, these individuals had been screened and given security clearance at the very highest level, so any concerns in this respect were negligible. Any security concerns of a more minor nature would not warrant the personal intervention of Sir David, so his involvement had to be for some unique situation or circumstance of a much higher level. Something so important that the British war effort may be compromised, or some political maneuverings between the Allied nations. Whatever it was, it involved Exercise “Tiger” and the American forces taking part.
In the wake of Sir David Petrie’s Plymouth visit, some very high level meetings were now taking place. On 12th April, Captain Glover of the staff of the Commander in Chief, United States Fleet, had luncheon with Admiral Moon, and the next day Lieutenant Commander Brauer was dispatched to London for a conference with staffs of Task Force 122 and Commander Naval Forces in Europe. There was something very important in the air. Again on 15th April Admiral Moon went aboard the USS “Ancon” to confer with Rear Admiral Hall, and two days later met again with British Admiral Leatham in Plymouth. This was unusually frequent liaison of the closest order and at the highest level for a military exercise, dealing with issues that clearly couldn’t be handled by staff officers.”
HMS "Azalea" commanded by Captain Geddes was the only escort vessel for convoy T-4 and has been criticised for his slow response to the German E-Boat attack. The reason for this may be because there was to be a defence exercise on the 18th and 19th of May where build-up elements of Forces “S”, “G” and “J” would assemble off the coast of Brighton on the assumption that a successful landing had taken place, and would then be subjected to attack by craft simulating E-Boats. A scenario the U.S. Navy knew of and was tempted to replicate in Lyme Bay.”
Admiral Moon officially interviewed Geddes after the attack … “ Did you notice anything distinguishing about the E-Boat tracers ? Blue tracers ?” Geddes replied … “ No, sir”. Significantly the German E-Boats were using red and yellow, so the reason for introducing the question of blue tracer suggests other vessels in the attack area were using that color. Despite his negative response, Geddes probably knew who was using blue tracer that night because he had been secretly briefed to expect a dummy attack.
E-Boat attack - German view