Autolycus or Sniffer was a

submarine detection system Submarine detection systems are an aspect of antisubmarine warfare. They are of particular importance in nuclear deterrence, as they directly undermine one of the three arms of the nuclear triad by making counter-force attacks on submarines possib ...

designed to detecting diesel-engined submarines from aircraft. It was designed to detect exhaust fumes from their diesel engines. Named after the mythical Greek, Autolycus, 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, where ...

, 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 develo ...

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 vast majority of the world's countries—including all of the great powers—forming two opposi ...

, 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, 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 snorkels, 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 t ...

were the first German submarines to operate primarily submerged. After the Second World War, this emphasis on submerged operation, battery capacity and higher submerged speed continued. In the US, the

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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 formed the basis for their ''Whiskey'' class. In the 1950s, the Fleet Air Arm were flying in the

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

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 t ...

in search of Whiskey, Zulu and Foxtrot submarines. Patrol aircraft operated from RAF Ballykelly 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 rese ...

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 potenti ...

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 (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

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

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and Echo II 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 , 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 , 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= Flight International , 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= Flight International , 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