The original snorkel suggestion was made by Prof. Walter in 1933, but not accepted. The Germans picked up some Dutch snorkel boats in 1940, but did not implement the technology. BTW, the Dutch used the snorkel as a cheap form of air conditioning for their Pacific submarines. The air in a submerged boat was cooler than in one running on the surface. It was not intended to avoid detection.

When he heard about the problems the U-boats were having, Prof. Walter again advised Doenitz to look at snorkels in a conversation on March 2, 1943. He looked into the problem theoretically and wrote a short report on May 19, 1943. Doenitz answered on May 27, 1943 in a letter telling Walter that his company would be involved in a project to get snorkels into the field. 10 years were wasted through lack of foresight.

The two main designs for snorkel heads which were looked at immediately was the ball valve and the ring valve. Both were purely mechanical in that they used a floating body to close the head. The ring valve was smaller than the ball valve, but the mechanism was soon broken by the action of the waves. The ball valve was more robust, but it reacted too often, leading to the pressure drop problem, and it was too big. However, it became the standard design. The T-valve was really a second generation device which separated the action of the valve from the action of the waves. It could be controlled through feed back loops and other sophisticated control systems.

The first two snorkel U-boats, U-264 and U-575 which were sent out in Feb. 1944 did not return. The third U-boat, U-667 left on March 8, 1944 and returned on May 19, 1944. These were all VIIC. The first IXC to return after 3 losses (U-543, 859 and 1222) was U-547 which left on April 30, 1944 and returned on August 13, 1944. It was a clear case of too little, too late. By end 1944, underwater records of up to 70 days had been set: U-315 and U-991 with 70 days, U-978 with 69 days and U-680 with 67 days.

The T-valve was developed in late 1944 and installed on 4 type II D boats (U-143, 145, 149 and 150) in March and April 1945. The evaluation was underway in the North Sea when the war ended. While looking at Roessler for this answer, I discovered again that my memory is not perfect. The T-valve did not make it on to the XXIII due to the calendar running out. The XXIII had a small ball valve snorkel head, sorry. The XXI also had a ball valve head. The point is that once the T-valve was evaluated, it would have replaced the ball valve as the standard snorkel later in 1945.

The snorkel head on the U-260 picture is a ball valve head. A small radar signature was a major design criteria for a snorkel head. That is why the ring valve design, which was also smaller than a ball valve, was tried.

\">You also state that \"the ball valve was missed 95% of the time by Allied radar\". Which type of radar are you referring to, 10cm, 3cm?<\" That comes from a reference I do not remember, but I suspect it was counting all snorkel boats. There were not that many (probably not more than 200 combat boats) which means it was both 10 and 3 cm radar since both were in use in 1944/45.

Regards,
SuperKraut