parsifal
Colonel
I believe it was actually in mid 1942 that the technology began to turn the tide.
In any event, it was only experienced, well-equipped ASW units that had any real effect.
During the crisis off the US seaboard, they were only able to sink the first U-boat in April, and during the first 6 months of the war there were only 3 or 4 sunk in US Atlantic waters. It was not ASW that limited the German offensive, it was a lack of U-boats to sink the dozens of available targets.
Not true. Experienced air units were needed to sink the boats, but as I pointed out to PB this was not the key function of air assets, it was to force the boat to submerge, become a static unit as a result, and provide adbvance warning and spotting services to the offensive hunter groups and the convoys alike.
Sinkings increased in the latter half of 1942, principally at the hands of the ASV night capable units of coastal command. U-Boats typically would surface at night to recharge their batteries, in the3 belief that they could not be spotted by the air patrols (particualrly in the bay Of biscay). With ASV the allies became adept at stalking the surfaced boat and then illuminating the taerget with either starshell or Leigh Lights, for the final run in. A lot of boats were lost until the introduction of the METOX Radar detection system
The first use of ASV Radar was in 1940, but the combination of leigh Light and ASV radar was not undertaken until the latter half of 1942. Wing Commander Humphry de Verde Leigh (later OBE DFC AFC) developed the Leigh light, effectively a powerful flood light steered by the ASV radar. This allowed ASV radar equipped aircraft to search for U-boats at night. The U-boat was initially tracked by the radar with the light following the radar track but switched off. Once the returns were lost, the light would be switched on and the U-boat would be bathed in light and very vulnerable, the first successful attack was on U502 on 5th July 1942. The sudden light was often the first indication that the U-boat had been found and the Leigh light was initially very successful, particularly in the Bay of Biscay.
Metox was the German answer to the Leigh light rendering it completely ineffective. The Metox sets received the transmitted pulses from the ASV and rendered them as audible beeps. It enjoyed the usual advantage of radar detectors over radar in that the signal is direct and only had to travel one way whereas the radar has to detect the very weak reflection from the submarine.[3]. Most radars increase the number of pulses and decrease the width of the pulses when switched to a shorter range, the shorter pulse widths allow the radar to look at closer objects. The Metox exploited the fact that once the radar operator changed the range indication from 36 miles to 9 miles (15 km), the pulse repetition frequency of the radar's transmitter doubled. Radar cannot detect any reflections returned earlier than half a pulse width so when the U-boat was closer than 9 miles the operator would change to the shorter scale. If the Metox set started beeping at twice the rate, the U-boat knew that they had been detected. By the time the aircraft approached the U-boat's position enough to energise the Leigh light, the U-boat was well under the water. As a bonus, the Metox set would also provide warning in excess of visual range in daylight.
Metox was eventually countered by a version of the 10 centimetre H2S which Metox couldn't detect and once again the Leigh light forced U-boat crews to refuse to run surfaced at night. Even during the day, the U-boats were easy prey as the new radar was easily able detect the U-boat's periscope.