meteorological intelligence

meteorological intelligence was essential to both sides in order to fight with the maximum effectiveness. It is impossible to overstress the importance of the weather in waging war, from launching a tactical attack to deciding when to start hostilities. As an example of the latter, weather conditions were a vital ingredient in the planning of Japan's move southwards in December 1941. War had to begin then, before the north-east monsoon in the South China Sea and the winter gales in the north Pacific reached their full strength, and while the Manchurian winter made Japan's northern flank comparatively safe from its traditional enemy, the USSR. The Japanese carrier force which attacked Pearl Harbor used bad weather to hide its approach, and at the start of the Coral Sea battle of May 1942 a cold front, with its associated cloud and poor visibility, concealed Yorktown's carrier aircraft as they approached their targets.

The use by the Japanese of a frontal system to cover their attack on Pearl Harbor resulted in the Americans employing meteorologists lavishly, with the Weather Wing of the US Army Air Forces (USAAF) eventually having more than 4,000 meteorologists in its weather squadrons world-wide. Meteorology was also considered sufficiently important for the Combined Chiefs of Staff to have their own meteorological committee. ‘Weather is a weapon,’ one expert is quoted in The US Army in World War II. The Signals Corps: The outcome ( G. Thompson and D. Harris, Washington, DC, 1966, p. 465). ‘If left to chance it may help you and the enemy, hurt both of you, or aid one of you and hinder the other. If it is properly used, the weather can be…on your side most of the time.’

To be accurate, meteorological intelligence has to be on a world-wide basis, and the German occupation of much of Europe, the Japanese seizure of much of the Pacific during the Pacific war, and the total secrecy of the USSR, denied large areas of the world to the western Allies during the early part of the war. Once the USSR joined the Allies, in June 1941, some progress was made in obtaining Soviet co-operation, an exchange of weather information being made between some Siberian stations and the USA. This information was far from complete, but certainly helped US operations in the north Pacific such as the Aleutian Islands campaigns, and was later extended to facilitate the delivery of Lend-Lease aircraft via the Alaskan–Siberian air route. But it was not until March 1944 that Soviet meteorological intelligence for operations against Germany became available to the West, when a reciprocal agreement was established which obtained data from 100 Soviet weather stations.

Accurate meteorological intelligence was most frequently required by air forces, and both the Americans and the British, apart from flying regular meteorological reconnaissance flights, used airborne meteorologists to fly ahead of their aircraft and report the weather over intended targets. In August 1943 the Germans inflicted heavy losses on American bombers when the fine weather predicted over Schweinfurt by German meteorologists showed it to be the USAAF's most likely target; and an accurate forecast of fine weather was also the key factor in launching Big Week in February 1944, which resulted in such heavy losses for the Luftwaffe over Germany. In the China–Burma–India theatre, the best meteorological intelligence that could at first be obtained for US pilots delivering supplies to China over the Hump was visual. ‘The present system,’ one pilot commented, ‘is that if you can see the end of the runway it's safe to take off.’ But even when proper meteorological intelligence was provided, aircraft continued to be lost in the atrocious flying conditions that prevailed over the Himalayas.

On land meteorological intelligence was needed by artillery units to fire accurately as ballistic adjustments had to be made to allow for wind direction and strength, and atmospheric pressure. It was also essential for launching ground offensives and to judge the condition of terrain. For example, accurate forecasts, as well as a thorough understanding of Lake Lagoda's ice surface, enabled the maximum amount of relief supplies to reach Leningrad across the lake's ice road during the winter of 1941–2; and an accurately predicted cold snap enabled Soviet tank forces, previously bogged down by rain and impassable roads, to launch a surprise offensive in the northern Caucasus during the winter of 1942.

In March 1943 the Japanese failed to repeat their success of using a weather front to screen their approach by sea when their meteorologists incorrectly predicted that poor visibility would hide from air reconnaissance their troopships taking reinforcements to New Guinea. The error compounded Allied foreknowledge of the operations through ULTRA intelligence and as a result the Japanese suffered heavy losses to Allied air power in the Bismarck Sea battle.

Allied amphibious and airborne operations against Lae during the New Guinea campaign also hinged on specific weather conditions. MacArthur's air commander, Lt-General George C. Kenney, required clear weather over the area for Allied aircraft, but fog over western New Britain and adjacent straits to hinder Japanese aircraft. Such conditions were not uncommon and though the American and Australian weather teams picked different dates as to when they would occur; Kenney chose the day between them and obtained the weather he needed.

Perhaps the best known example of momentous events hanging on accurate meteorological intelligence was the Normandy landings (see OVERLORD). Allied meteorologists correctly predicted a gap in the poor weather—a prediction helped by information supplied by aircraft and warships specially stationed in the Atlantic—which enabled Eisenhower to launch OVERLORD on 6 June, while the failure of their German counterparts to predict the gap led to a relaxation of German vigilance. However, German weather reports were certainly accurate when the Ardennes campaign was launched on 16 December 1944: Hitler stated that meteorological intelligence obtained from U-boats in the Atlantic ‘contributed decisively’ to the initial success of the offensive because it was started in low cloud which neutralized Allied air power.

As in so many other fields of scientific endeavour, meteorology developed swiftly during the course of the war. By 1944 the Allies were employing ‘sferic’ (an abbreviation of atmospherics) equipment which, could take bearings on the lightning a storm caused up to 1,600 km. (1,000 mi.) away, far beyond the range of radar. Along with a radio direction finder called a Rawin, radar was by then being used to track hydrogen balloons, the basic tool of the meteorologist on both sides. Tracked by theodolite, these balloons indicated the speed and direction of the wind in the upper atmosphere. They were also used to take radiosondes into the upper atmosphere to measure temperature, pressure, and humidity. Lack of atmospheric pressure eventually caused the balloon to burst and the radiosonde, still recording the information, then descended by parachute. By 1944 the Americans had developed a radiosonde which transmitted the information back to its controller.

It was the positioning of meteorological teams employing this equipment, or of automatic weather stations transmitting meteorological information, which caused what might be termed the ‘weather war’. This was waged in the Atlantic and Arctic by the Allies against German meteorological teams and weather ships whose information, supplemented by weather flights, was of great assistance to the Luftwaffe opposing the Allied strategic air offensives in Europe. Meteorological parties were dispatched by the Abwehr to Greenland, Spitzbergen, and other Arctic islands. Because the British Code and Cypher School at Bletchley Park had broken the Abwehr's hand cipher, the early parties were all captured, but some later ones, as well as unmanned stations, were successfully established by the German Navy. The teams were all pinpointed eventually, some of them from ULTRA intelligence. ULTRA was also responsible for capturing two German weather ships, both of which yielded vital cryptographic information, but one of the unmanned stations, established on Canada's Labrador coastline, remained unidentified until 1981. On Spitzbergen, where one German team flew daily reconnaissance flights, German and Norwegian meteorologists clashed in a number of running fights. Another German team fought off the Greenland Sledge Patrol before long-range US bombers forced its evacuation months later. Its successor, perhaps because it supplied Bletchley Park with useful ULTRA intelligence, remained unmolested from August 1943 to April 1944, but two others, dispatched to Greenland in August and September 1944, were quickly rounded up by the US Coast Guard.

Bibliography

Stagg, J. , Forecast for Overlord (Shepperton, 1971).