Radar picket
A radar picket is a radar-equipped station, ship, submarine, aircraft, or vehicle used to increase the radar detection range around a nation or military force to protect it from surprise attack, typically air attack, or from criminal activities such as smuggling. The term 'picket' is an old military term for a sentry placed forward of a defensive line, in order to provide an advanced warning. By definition a radar picket must be some distance removed from the anticipated targets to be capable of providing early warning. Often several detached radar units would be placed in a ring to encircle a target to provide increased cover in all directions; another approach is to position units to form a barrier line.
Radar picket units may also be equipped to direct friendly aircraft to intercept any possible enemy. In British terminology the radar picket function is called aircraft direction. A ship performing this function is termed a fighter direction ship. Airborne radar pickets are referred to as Airborne early warning and control or simply airborne early warning, depending on capabilities.
In a sense radars intended to track ballistic missiles can be thought of as radar pickets, but because such systems also came to be used for tracking orbital satellites and space debris the current preferred term for them is space domain awareness systems.
World War II
United Kingdom World War II radar pickets
UK coastal radar
or CH was the codename for the ring of coastal early warning radar stations built by the Royal Air Force before and during World War II to detect and track aircraft. Chain Home proved decisive during the Battle of Britain in 1940. The Chain Home network was continually expanded, with over 40 stations operational by the war's end. CH was not able to detect aircraft at low altitude, and from 1939 was normally partnered with the Chain Home Low system which could detect aircraft flying at any altitude over. Ports were covered by Chain Home Extra Low, which gave cover down to but at shorter ranges of approximately. In 1942 the AMES Type 7 radar began to assume the job of tracking of targets once detected, and CH moved entirely to the early warning role.UK World War II AEW&C
In late 1944 the Fighter Interception Development Squadron carried out operational trials under Operation Vapour of a Vickers Wellington which was equipped with a modified ASV Mk VI radar set and PPI, as one of the first Airborne Early Warning and Control aircraft. It operated at an altitude of 4,000 feet over the North Sea to control de Havilland Mosquito and Bristol Beaufighter night fighters intercepting Heinkel He 111 bombers flying from Dutch airbases and their V-1 flying bombs. The Wellington was fitted with a homing beacon so the night fighters could locate and keep station with it. Despite encouraging results, the operational trials ended after the Luftwaffe stopped air launches by mid January 1945.German World War II radar pickets
Kammhuber Line
The Kammhuber Line was the Allied name given to the German night air defense system established in July 1940 by Colonel Josef Kammhuber. The first version of the Line consisted of a series of 'boxes' of radar stations with overlapping coverage, layered three deep from Denmark to the middle of France, each covering a zone about 32 km long and 20 km wide. Each station consisted of a control center with a FuMG A1 Freya radar with a range of about 100 km and a directed searchlight for the night fighters. Later versions of the Line added two Würzburg-Riese radars, with a range of about 30 km. Unlike the early-warning Freya, Würzburgs were accurate tracking radars. One Würzburg would lock onto the target as soon as the Freya picked it up, and the second Würzburg would lock onto the night fighter as soon as it entered the box, thereby allowing controllers to get continual readings of the positions of both planes.The Line was very effective against early RAF Bomber Command tactics. However, on the night of 30/31 May 1942 in its 1,000 plane raid against Cologne, Bomber Command introduced the use of the bomber stream. The concentration of bombers through a few of the boxes resulted in the defenses being overwhelmed. In response, the Germans converted their ground radar into a radar network, which would follow the path of the British bombers, while a controller directed the night fighters into the stream. Measure and counter measure continued until October 1944, when German defenses were no longer able to respond to Germany's deteriorating situation.
''Kriegsmarine''
From 1943 Nazi Germany's Kriegsmarine operated several radar-equipped night fighter guide ships, including the NJL Togo. which was equipped with a Freya radar for early warning and a Würzburg-Riese gun laying radar, plus night fighter communications equipment. From October 1943, Togo cruised the Baltic Sea under the operational control of the Luftwaffe. In March 1944, after the three great Soviet bombing raids on Helsinki, she arrived in the Gulf of Finland to provide night fighter cover for Tallinn and Helsinki.Japanese World War II radar pickets
The Imperial Japanese Navy briefly modified two submarines as dedicated radar pickets in the first half of 1945, but reconverted them to an even more important role as tanker submarines in June of that year.United States World War II radar pickets
US Navy
Radar picket ships first came into being in the US Navy during World War II to aid in the Allied advance to Japan. The number of radar pickets was increased significantly after the first major employment of kamikaze aircraft by the Japanese in the Battle of Leyte Gulf in October 1944. and destroyers with SGA and SC radars were pressed into picket service with few modifications at first – the Allen M. Sumners were the first destroyers to be designed with a combat information center, which made them ideal for this use. Later, additional radars and fighter direction equipment were fitted, along with more light anti-aircraft guns for self-defense, usually sacrificing torpedo tubes to make room for the new equipment, particularly the large SP height-finding radars of the era. Deploying some distance from the force to be protected along likely directions of attack, radar pickets were the nearest ships to the Japanese airfields. Thus, they were usually the first vessels seen by incoming waves of kamikazes, and were often heavily attacked.The radar picket system saw its ultimate development in World War II in the Battle of Okinawa. A ring of 15 radar picket stations was established around Okinawa to cover all possible approaches to the island and the attacking fleet. Initially, a typical picket station had one or two destroyers supported by two landing ships, usually landing craft support or landing ship medium , for additional AA firepower. Eventually, the number of destroyers and supporting ships were doubled at the most threatened stations, and combat air patrols were provided as well. In early 1945, 26 new construction s were ordered as radar pickets without torpedo tubes, to allow for extra radar and AA equipment, but only some of these were ready in time to serve off Okinawa. Seven destroyer escorts were also completed as radar pickets.
The radar picket mission was vital, but it was also costly to the ships performing it. Out of 101 destroyers assigned to radar picket stations, 10 were sunk and 32 were damaged by kamikaze attacks. The 88 LCSs assigned to picket stations had two sunk and 11 damaged by kamikazes, while the 11 LSMs had three sunk and two damaged.
The high casualties off Okinawa gave rise to the radar picket submarine, which had the option of diving when under attack. It was planned to employ converted radar picket submarines should the invasion of Japan become necessary. Two submarines received rudimentary conversions during the war with the new SR search radars and the SV search radars mounted vertically as height finders, and two others were completed immediately after the war with the same suite, but none were used postwar in this role.
Cold War
United States and Canada
During the Cold War, the Royal Canadian Air Force and the United States Air Force jointly built and operated radar picket stations to detect Soviet bombers, and the United States Navy expanded the naval radar picket concept. The wartime radar picket destroyers were retained, and additional DDRs, destroyer escorts, submarines, and auxiliaries every carrier group would have radar pickets deployed around it for early warning of the increasing threat of Soviet air-to-surface missile attack, and 2) radar pickets would form barriers off the North American coasts, thus extending the land based lines. While on station, all of these assets – other than those assigned to fleet defense – were operationally controlled by the Aerospace Defense Command and after May 1958 NORAD.Fixed installations
During the 1950s the governments of Canada, Denmark, and the United States built three lines of fixed radar picket sites across Canada, and with the DEW Line into Alaska and Greenland. These were the Pinetree Line, the Mid-Canada Line, and the Distant Early Warning Line. The DEW Line would be equipped with AN/FPS-19, and until 1965 AN/FPS-23 radars. There was also a line of radar sites in Alaska extending westward from the end of the DEW Line to the end of the Aleutian Islands, and a line eastward from the Greenland end of the DEW Line to Iceland, the Faroe Islands, and Scotland.There were also three oil-rig-type offshore radar stations known as "Texas Towers" off the New England coast with AN/FPS-3 and AN/FPS-6 radars.
While not designed as pickets per se, coastal and interior fixed radars such as the interim Lashup Radar Network, the Permanent System, and Semi-Automatic Ground Environment , would function as pickets for areas removed from suspected airborne attackers.