Autolycus or Sniffer was a submarine detection system designed to detecting diesel-engined submarines from aircraft. It was designed to detect exhaust fumes from their

diesel engines The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-cal ...

. Named after the mythical Greek,

Autolycus In Greek mythology, Autolycus (; Ancient Greek: Αὐτόλυκος ''Autolykos'' 'the wolf itself') was a successful robber who had even the power of metamorphosing both the stolen goods and himself. He had his residence on Mount Parnassus and ...

, who took part in the search for the

Golden Fleece In Greek mythology, the Golden Fleece ( el, Χρυσόμαλλον δέρας, ''Chrysómallon déras'') is the fleece of the golden-woolled,, ''Khrusómallos''. winged ram, Chrysomallos, that rescued Phrixus and brought him to Colchis, wh ...

, it was developed by the British during the early Cold War period. The first version of Autolycus was deployed on

Avro Shackleton The Avro Shackleton is a British long-range maritime patrol aircraft (MPA) which was used by the Royal Air Force (RAF) and the South African Air Force (SAAF). It was developed by Avro from the Avro Lincoln bomber, which itself had been a devel ...

aircraft in the mid-1950s, with an improved version re-appearing in the mid-1960s.

Submarines

Until the end of the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

, submarines spent the majority of the time on the surface, powered by their diesel engines. They could submerge for only short periods during and after the attack. This made them easy to detect on

radar Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...

, and by 1943, radar-equipped aircraft had made surface submarine operations difficult. Just before the outbreak of the Second World War, the Royal Netherlands Navy introduced the first

submarine snorkel A submarine snorkel is a device which allows a submarine to operate submerged while still taking in air from above the surface. British Royal Navy personnel often refer to it as the snort. A concept devised by Dutch engineers, it was widely use ...

s, which provided air to the crew and the engines, allowing the submarine to remain submerged just below the surface. This allowed them to avoid most radars, as well as allowing them to approach convoys more closely on diesel, extending the range they could run on batteries. When Nazi Germany invaded and occupied the Netherlands in 1940 they also captured the latest Dutch submarines O-21 class equipped with snorkels, which the Germans then copied and started to use from 1943 onwards. Designs like the

Type XXI U-boat Type XXI submarines were a class of German diesel–electric '' Elektroboot'' (German: "electric boat") submarines designed during the Second World War. One hundred and eighteen were completed, with four being combat-ready. During the war only ...

were the first German submarines to operate primarily submerged. After the Second World War, this emphasis on submerged operation,

battery capacity An electric battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. When a battery is supplying power, its positive terminal is the cathode and its neg ...

and higher submerged speed continued. In the US, the

GUPPY The guppy (), also known as millionfish and rainbow fish, is one of the world's most widely distributed tropical fish and one of the most popular freshwater aquarium fish species. It is a member of the family Poeciliidae and, like almost al ...

program rebuilt wartime submarines to emphasise these features. In the

Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...

, the four Type XXIs that were assigned to them by the

Potsdam Agreement The Potsdam Agreement (german: Potsdamer Abkommen) was the agreement between three of the Allies of World War II: the United Kingdom, the United States, and the Soviet Union on 1 August 1945. A product of the Potsdam Conference, it concerned t ...

formed the basis for their ''Whiskey'' class. In the 1950s, the

Fleet Air Arm The Fleet Air Arm (FAA) is one of the five fighting arms of the Royal Navy and is responsible for the delivery of naval air power both from land and at sea. The Fleet Air Arm operates the F-35 Lightning II for maritime strike, the AW159 Wil ...

were flying in the

North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...

and the

GIUK gap The GIUK gap (sometimes written G-I-UK) is an area in the northern Atlantic Ocean that forms a naval choke point. Its name is an acronym for ''Greenland, Iceland'', and the ''United Kingdom'', the gap being the two stretches of open ocean betwe ...

for patrol and potentially

anti-submarine warfare Anti-submarine warfare (ASW, or in older form A/S) is a branch of underwater warfare that uses surface warships, aircraft, submarines, or other platforms, to find, track, and deter, damage, or destroy enemy submarines. Such operations are typi ...

in search of Whiskey, Zulu and

Foxtrot The foxtrot is a smooth, progressive dance characterized by long, continuous flowing movements across the dance floor. It is danced to big band (usually vocal) music. The dance is similar in its look to waltz, although the rhythm is in a ti ...

submarines. Patrol aircraft operated from

RAF Ballykelly Royal Air Force Ballykelly or more simply RAF Ballykelly is a former Royal Air Force station which opened in 1941 in Ballykelly, County Londonderry. It closed in 1971 when the site was handed over to the British Army as Shackleton Barracks. A s ...

in Northern Ireland. A means was needed for the initial detection of submarines in the area. Once detected, other methods such as radar or

sonobuoy A sonobuoy (a portmanteau of sonar and buoy) is a relatively small buoy – typically diameter and long – expendable sonar system that is dropped/ejected from aircraft or ships conducting anti-submarine warfare or underwater acoustic resear ...

hydrophone A hydrophone ( grc, ὕδωρ + φωνή, , water + sound) is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates an electric potent ...

s could be used to track and target the contact.

Operation

Autolycus was an ion-mobility spectrometer (IMS). This is an early technique of extreme sensitivity and was a major technique for the initial detection of an unseen submarine. An IMS measures how fast a given ion moves in a uniform electric field through a given atmosphere. The spectrometer separates ions by shape and charge, so that different species arrive at the detector at different times. Typically this is used to produce a mobility profile characterising the sample. For Autolycus, a boxcar integrator sampled the times for known markers within diesel exhaust. Display to the operator was on a continuous paper printout. The Autolycus technique was developed and first tested during the Second World War on warships. After the war, the Mk. II version became light enough for airborne use. Fast-moving aircraft were better able to locate submarines by travelling in search patterns. Early Mk II versions of Autolycus suffered from calibration difficulties in high humidity and stopped working altogether in rain. These problems were reduced in the Mk. III version. This also had better time discrimination, giving better position fixes. On the Shackleton the air scoop for the system was located on the port side of the aircraft nose.

Search patterns

As Autolycus detected fumes from the submarine, rather than sound emanating from the hull, it could detect the passage of a submarine for some time after it had passed. This aided searching, as it did not need to pass directly overhead. A zig-zag search pattern was flown, passing at right-angles over the likely direction of submarine movements. When an exhaust plume was detected, the aircraft would begin to fly a tracking pattern of progressively shorter zig-zags. Each crossing of the plume trail would be plotted, giving a map plot of the submarine's likely track. As the track was narrowed down, the aircraft would switch sensors to a more precise method, such as centimetric radar or dropping

s before potentially closing for an attack.

Withdrawal

Autolycus was withdrawn for a number of reasons. The most immediate one was the withdrawal of the Shackleton carrier aircraft and their replacement with the Nimrod MR1. Nimrod was fitted with Autolycus, but this legacy equipment was no longer considered to be a first-line technique and so it was not integrated into the new tactical display system, based on an Elliott 920 digital computer. The Nimrod was equipped with a

Magnetic Anomaly Detector A magnetic anomaly detector (MAD) is an instrument used to detect minute variations in the Earth's magnetic field. The term refers specifically to magnetometers used by military forces to detect submarines (a mass of ferromagnetic material cr ...

(MAD) tail boom. MAD was considered to be more capable than the Autolycus approach and could also detect submerged submarines operating without diesels or the increasing threat from nuclear submarines. MAD had not been successfully fitted to the Shackleton, possibly because of interference problems from the piston engines and their ignition system. Although the main submarine threat at the time of Autolycus' withdrawal was still the Soviet diesel-engine

Golf Golf is a club-and-ball sport in which players use various clubs to hit balls into a series of holes on a course in as few strokes as possible. Golf, unlike most ball games, cannot and does not use a standardized playing area, and coping ...

and Juliett class submarines, increasing numbers of the nuclear-powered

Hotel A hotel is an establishment that provides paid lodging on a short-term basis. Facilities provided inside a hotel room may range from a modest-quality mattress in a small room to large suites with bigger, higher-quality beds, a dresser, a ref ...

and

Echo II Echo II or Echo 2 or ''variant'', may refer to: * ''Echo II''-class submarine of the Soviet Navy * Echo 2 (satellite), a 1964 NASA communications satellite * Echo II (expansion card), a speech synthesizer card for the Apple II See also * EchoSt ...

were in service in this region. As these did not need to snorkel and did not produce diesel exhaust they were effectively undetectable by either the Shackleton's Autolycus or its ASV Mk 13 radar. One of the cited limitations for Autolycus was a lack of discrimination between submarine exhaust, trawlers and on-shore sources. In practice this does not appear to have been a major limitation as it was used for initial detection, not identification or tracking.

References

{{Reflist, colwidth=35em, refs= {{Cite book , title=Nimrod's Genesis , last=Gibson , first=Chris , publisher=Hikoki Publications , year=2015 , isbn=978-190210947-3 , pages=22–24 {{Cite book , title=The Naval Institute Guide to World Naval Weapons Systems, 1997-1998 , page=662 , isbn=9781557502681 , url=https://books.google.com/books?id=l-DzknmTgDUC&q=Autolycus&pg=PA662 , last1=Friedman , first1=Norman , year=1997 {{Cite web , title=Ballykelly's Shackleton Era 1952–1971 , url=http://www.home.aone.net.au/shack_one/balkela.html , year=2001 , archive-url=https://web.archive.org/web/20040225112109/http://www.home.aone.net.au/shack_one/balkela.html , archive-date=2004-02-25 {{Cite book , title=Ion Mobility Spectrometry, Second Edition , author=G.A. Eiceman, Z. Karpas , publisher=

CRC Press The CRC Press, LLC is an American publishing group that specializes in producing technical books. Many of their books relate to engineering, science and mathematics. Their scope also includes books on business, forensics and information tec ...

, year=2005 , isbn=0-8493-2247-2 , page=12 , url=https://books.google.com/books?id=XEstH8BZq5cC&q=Autolycus+submarine&pg=PA12 {{Cite journal , journal=

Flight International ''Flight International'' is a monthly magazine focused on aerospace. Published in the United Kingdom and founded in 1909 as "A Journal devoted to the Interests, Practice, and Progress of Aerial Locomotion and Transport", it is the world's olde ...

, date=30 September 1971 , page=547 , title=Avionics , author=John Marriott , url=http://www.flightglobal.com/pdfarchive/view/1971/1971%20-%202019.html , quote=There are two other methods of detecting a submerged submarine from the air. The first, called Autolycus in Britain and Sniffer in America, is a device which detects the fumes emitted by a diesel-powered submarine into the atmosphere. It is not a primary means of detection and at best it can only tell the aircraft that a diesel submarine was recently present (and has now dived), or is present but for some reason the snorkel has not been detected. As more and more submarines become nuclear powered the device will lose its already limited usefulness. {{Cite web , url=http://discovery.nationalarchives.gov.uk/SearchUI/details?Uri=C11291211 , title=Report on experience with Autolycus Mk 2 against snorting submarines. , id=DEFE 67/112 , publisher=DEFE Records of the Ministry of Defence, Records of Scientific Research , author=DEFE 67 Ministry of Defence (Navy): Operational Evaluation Group and Submarine Tactics and Weapons Group, and Joint Anti-Submarine School (JASS): Reports and Notes , year=1957 {{Cite journal , title=Airborne Watchkeeper , first=John , last=Bentley , journal=

, date=27 November 1969 , page=847 , url=https://www.flightglobal.com/pdfarchive/view/1969/1969%20-%203301.html?search=%22orange%20harvest%22 {{Cite journal , title=Nimrod: Systematic Sub Hunter , journal=

, last=Neal , first=Molly , volume=97 , issue=3176 , date=22 January 1970 , page=127 , url=https://www.flightglobal.com/pdfarchive/view/1970/1970%20-%200155.html Cold War military equipment of the United Kingdom Anti-submarine warfare Submarine detection systems Military sensor technology Naval weapons of the United Kingdom 1950s establishments