Operation Outward was a British campaign of the Second World War that attacked Germany and German-occupied Europe with free-flying balloons. It made use of cheap, simple balloons filled with hydrogen and carrying either a trailing steel wire to damage high-voltage power lines by producing a short circuit, or incendiary devices to start fires in fields, forests and heathland. A total of 99,142 Outward balloons were launched; about half carried incendiaries and half carried trailing wires. Compared to Japan's better-known fire balloons, Outward balloons were crude. They had to travel a much shorter distance so they flew at a lower altitude – 16,000 ft (4,900 m), compared with 38,000 ft (12,000 m) – and had only a simple mechanism to regulate altitude by means of dropping ballast or venting lifting gas. This meant the balloons were simple to mass-produce and only cost £1 15/- each (approximately equivalent to £85 in 2025). The free flying balloon attacks were highly successful. Although difficult to assess exactly, their economic impact on Germany was far in excess of the cost to the British government.
History and development
Because there was concern over what could happen if a barrage balloon accidentally got loose, in 1937 the British carried out a study on the damage that may be caused by a balloon-carried wire hitting power lines. These concerns were evidently borne out when early in 1940, the Air Vice Marshal Balloon Command, the organisation responsible for the barrage balloons, wrote that "Since the outbreak of the war, I have had constant complaints from the electricity distributors regarding the damage done in this country by [barrage] balloons that have broken away from their moorings". to which he added "...advantage might be taken of this to impede and inconvenience the enemy". It was proposed that bomb-laden balloons could be launched from France. Their position would be tracked by radio triangulation and the bombs would be released by radio control when the balloon drifted over a worthwhile target. This plan was never put into action; objections included that "attacks of this nature should not be originated from a cricketing country" and a concern that the enemy might retaliate with similar weapons. The idea became redundant when defeat in the Battle of France put possible launch sites out of British control.
On the night of 17/18 September 1940, a gale broke loose a number of British barrage balloons and carried them across the North Sea. In Sweden and Denmark, they damaged power lines, disrupted railways and knocked down the antenna for the Swedish International radio station. Five balloons were reported to have reached Finland. A report on the damage and confusion reached the British War Cabinet on 23 September 1940. Winston Churchill then directed that the use of free-flying balloons as weapons against Germany should be investigated. The Air Ministry initially produced a negative report, possibly because the Ministry of Aircraft Production felt balloons would be ineffective weapons and would consume too many resources.
The Admiralty took up the idea with more enthusiasm. In particular, Captain Gerald Banister, Director of Boom Defence and a proponent of using balloons as a weapon of offence, pressed the point. The meteorological considerations – including the possibility that the weather might favour the enemy retaliating in kind – were carefully investigated and found to be highly favourable; winds above 16,000 feet (4,900 m) tend to blow from west to east, making it difficult for the Germans to retaliate with similar balloons. Of particular interest was the possibility of damaging Germany's electricity distribution network by shorting high-voltage overhead power lines with thin wires dragged by balloons. The results of investigations were favourable: trials showed that even a thin steel wire, much thinner than that used to tether the static barrage balloons, when drawn in sliding contact across two or more phases, could cause an arc as long as 15 ft (4.6 m) and that arc would be maintained until the circuit breaker opened. In some cases, the arc's heat could melt the aluminium outer layers and then the reinforcing steel centre strands of the conductors. Even if the cable was not severed, the conductors would be weakened so that they would be susceptible to breaking due to increased electrical demand or normal weather events such as wind, snow and ice. Investigations revealed that it was common in pre-war Germany to use a Petersen coil as protection against earthing; this design was effective against a short between a high-voltage cable and earth but relatively vulnerable to a short between different phases. A short between phases could result in damage, not just to a cable but to transformers and the circuit breakers. The Admiralty ran trials using surplus spherical latex meteorological balloons about 8 ft (2.4 m) in diameter when inflated. Calculations based on the trials predicted that there would be between a 10% to 75% chance of a balloon's wire coming into contact with a high-voltage overhead line during a 30 mi (48 km) flight along the ground. Balloons could also carry incendiaries. Large areas of pine forest and heathland in Germany made the countryside vulnerable to random incendiary attack and it was hoped that the Germans would be forced to assign large numbers of people to the task of fire watching, possibly diverting them from more productive war-work. The Admiralty concluded that the balloons could be produced at very little cost; many of the important parts already existed as surplus materials and despite the needs of conventional barrage balloons, there was plenty of hydrogen gas with which to fill the balloons. The balloons could be used with a small number of British personnel who would face minimal risks.
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