Metox
Encyclopedia
The Metox, named after its manufacturer, was a pioneering high frequency very sensitive radar warning receiver
(RWR) manufactured by a small French company in occupied Paris, which could detect ASV (Air to Surface Vessel radar
) transmissions from patrolling Allied aircraft
. It is not clear whether the design was German or French or both. It was installed on German
U-boat
s during World War II
from 1942.
From July 1940 onwards, the British fitted the RAF Mk II AI (Airborne Interception) radar into Coastal Command aircraft for use as the MkII "1½-metre ASV". The radar's known AI weaknesses — problems due to land clutter
and inability to determine height effectively, which caused its failure in night fighters — were no handicap in this new role. With two range scales, 0–9 and 0–36 miles, it could detect surfaced U-boats at up to 12 miles (19.3 km) and land at up to 70 miles, though a typical U-boat detection range was 5 miles. The radar had a fairly crude display by today's standards, but was able to give the range and an approximate direction within an arc either side of the aircraft heading. Returns were lost in sea clutter once the aircraft was within about 1 mile of the U-boat, but usually by then, the aircraft was within visual range —- and the U-boat was well into a crash dive
.
To counter this, Wing Commander Humphry de Verde Leigh (later OBE
DFC
AFC
) developed the Leigh light
, effectively a powerful floodlight 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 the on 5 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 British radar, 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. 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 (57.9 km) to 9 miles (14.5 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 (14.5 km) 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 was close enough to the U-boat's position 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 radar
which Metox could not detect and once again the Leigh light forced U-boat crews to refuse to run surfaced at night. Even during the day the new radar was easily able to detect a submerged U-boat's periscope
or snorkel
, assuming they were deployed, which earlier radars employing longer wavelengths could not do.
Metox was superseded by the Naxos
receiver that was capable of detecting centimetric radar.
Radar warning receiver
Radar warning receiver systems detect the radio emissions of radar systems. Their primary purpose is to issue a warning when a radar signal that might be a threat is detected. The warning can then be used, manually or automatically, to evade the detected threat...
(RWR) manufactured by a small French company in occupied Paris, which could detect ASV (Air to Surface Vessel radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
) transmissions from patrolling Allied aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
. It is not clear whether the design was German or French or both. It was installed on German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
U-boat
U-boat
U-boat is the anglicized version of the German word U-Boot , itself an abbreviation of Unterseeboot , and refers to military submarines operated by Germany, particularly in World War I and World War II...
s during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
from 1942.
From July 1940 onwards, the British fitted the RAF Mk II AI (Airborne Interception) radar into Coastal Command aircraft for use as the MkII "1½-metre ASV". The radar's known AI weaknesses — problems due to land clutter
Clutter (radar)
Clutter is a term used for unwanted echoes in electronic systems, particularly in reference to radars. Such echoes are typically returned from ground, sea, rain, animals/insects, chaff and atmospheric turbulences, and can cause serious performance issues with radar systems.- Backscatter coefficient...
and inability to determine height effectively, which caused its failure in night fighters — were no handicap in this new role. With two range scales, 0–9 and 0–36 miles, it could detect surfaced U-boats at up to 12 miles (19.3 km) and land at up to 70 miles, though a typical U-boat detection range was 5 miles. The radar had a fairly crude display by today's standards, but was able to give the range and an approximate direction within an arc either side of the aircraft heading. Returns were lost in sea clutter once the aircraft was within about 1 mile of the U-boat, but usually by then, the aircraft was within visual range —- and the U-boat was well into a crash dive
Crash dive
A crash dive is a maneuver performed by a submarine to submerge as quickly as possible to avoid attack. Crash diving from the surface to avoid attack has been largely rendered obsolete with the advent of nuclear-powered submarines as they operate constantly submerged and are unlikely to be found on...
.
To counter this, Wing Commander Humphry de Verde Leigh (later OBE
Order of the British Empire
The Most Excellent Order of the British Empire is an order of chivalry established on 4 June 1917 by George V of the United Kingdom. The Order comprises five classes in civil and military divisions...
DFC
Distinguished Flying Cross (United Kingdom)
The Distinguished Flying Cross is a military decoration awarded to personnel of the United Kingdom's Royal Air Force and other services, and formerly to officers of other Commonwealth countries, for "an act or acts of valour, courage or devotion to duty whilst flying in active operations against...
AFC
Air Force Cross (United Kingdom)
The Air Force Cross is a military decoration awarded to personnel of the United Kingdom Armed Forces, and formerly also to officers of the other Commonwealth countries, for "an act or acts of valour, courage or devotion to duty whilst flying, though not in active operations against the enemy"...
) developed the Leigh light
Leigh light
The Leigh Light was a British World War II era anti-submarine device used in the Second Battle of the Atlantic.It was a powerful carbon arc searchlight of 24 inches diameter fitted to a number of the British Royal Air Force's Coastal Command patrol bombers to help them spot surfaced...
, effectively a powerful floodlight 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 the on 5 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
Bay of Biscay
The Bay of Biscay is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Brest south to the Spanish border, and the northern coast of Spain west to Cape Ortegal, and is named in English after the province of Biscay, in the Spanish...
.
Metox was the German answer to the British radar, 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. 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 (57.9 km) to 9 miles (14.5 km), the pulse repetition frequency
Pulse repetition frequency
Pulse repetition frequency or Pulse repetition rate is the number of pulses per time unit . It is a measure or specification mostly used within various technical disciplines Pulse repetition frequency (PRF) or Pulse repetition rate (PRR) is the number of pulses per time unit (e.g. Seconds). It...
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 (14.5 km) 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 was close enough to the U-boat's position 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 radar
H2S radar
H2S was the first airborne, ground scanning radar system. It was developed in Britain in World War II for the Royal Air Force and was used in various RAF bomber aircraft from 1943 to the 1990s. It was designed to identify targets on the ground for night and all-weather bombing...
which Metox could not detect and once again the Leigh light forced U-boat crews to refuse to run surfaced at night. Even during the day the new radar was easily able to detect a submerged U-boat's periscope
Periscope
A periscope is an instrument for observation from a concealed position. In its simplest form it consists of a tube with mirrors at each end set parallel to each other at a 45-degree angle....
or snorkel
Submarine snorkel
A submarine snorkel is a device which allows a submarine to operate submerged while still taking in air from above the surface. Navy personnel often refer to it as the snort.-History:...
, assuming they were deployed, which earlier radars employing longer wavelengths could not do.
Metox was superseded by the Naxos
Naxos radar detector
The FuG 350 Naxos radar warning receiver was a World War II German countermeasure to SHF band centimetric wavelength radar produced by a cavity magnetron...
receiver that was capable of detecting centimetric radar.