'Petard' was the British later development of 'Albino' (18 March/November 1942).

Related to 'Albino' and 'Outward' (i), this undertaking was used in an effort to bring down German bombers by use of a series of balloons each with an aerial mine attached to it. The operational concept was that when a German raid was taking place, a vast number of these balloons would be released from the ground into the path of the bombers, the time of launch having to be calculated very carefully as success depended on the use of the wind to carry the slowly rising balloons into the path of the bombs.

The first trial was made by No. 30 Balloon Group over the Thames river estuary from 10.00 onward on 7 February 1942 in an attempt to attack German minelaying aircraft.

The weapon was exactly the same as that used in 'Albino' with the exception of the fact that the release of the brake on the spool of wire, which carried the bomb at its lower end, by fuse action was set at a lower specific height as the balloon rose into the air. It was ordered that the balloons would be set to fly at a minimum height of 4,500 ft (1370 m), and the self-destruct fuses were designed to go off at 45-minute intervals, depending on the wind speed: as the wind speed increased the self-destruct fuse burned faster.

The balloons were to be released when the wing was from the south-south-east, from 'Fronts' (land sites) on the coast between Margate and Sheppey to the south of the planned interception area, and Shoeburyness and the Naze to the north-west of the area. There were two squadron fronts in the form of North Squadron based to the north of the Thames river and South Squadron based to the south of the same river.

On the night of 7/8 February 1942, Air Marshal Sir Leslie Gossage’s Balloon Command stood by waiting for the order to release from the headquarters of Air Marshal Sir William Sholto Douglas’s Fighter Command. All British aircraft were warned to stay away from the area and al British naval vessels received the same warning. The headquarters of Lieutenant General Sir Frederick Pile’s Anti-Aircraft Command was also ordered to instruct its units not to use their searchlights during the duration of the operation.

Ground-controlled interception and and the Chain Home Low radar network were expected to monitor the Petard units for both height and direction.

The 'Petard' balloon system was first used against German aircraft on the night of 18/19 March 1942. South Squadron at Swalecliffe, near Herne Bay on the north coast of Kent, was ready at 18.36, and the first plots of German bombers were made by Fighter Command headquarters at 19.56 when the bombers were some 45 miles (72.5 km) off the Hoek van Holland. At 20.01 the order to stand-by was given, and the ground crews began to inflate their balloons in their release tents. As the number of oncoming German bombers increased, Balloon Command gave the order to release at 21.00. Some 12 German aircraft arrived over the UK, and departed the Thames river estuary at 20.52, none of them having succumbed to a 'Petard' balloon.

The cease-fire was ordered. The weather over the Netherlands was currently reported as bad, and as no further radar plots were seen it was decided to stand down the balloon squadrons, which then returned to base. At 21.42 a second wave of eight German aircraft appeared, but there was no way for the balloons to be released against these. No German aircraft appeared to have been hit, but one radar plot faded some 15 miles (24 km) out to sea, so it is conceivable that it might have been damaged. One other aircraft behaved quite strangely and circled around for almost an hour, presumably in difficulties, but eventually headed for home.

Some 450 balloons had been released. Though set to fly at 4,500 ft (1370 m), one or two of them reached 11,000 ft (3355 m) because their wires broke and their reduced weight allowed them to climb to a greater height.

Another attempt took place on 31 March/1 April 1942. The weather was ideal for a release, and as no German aircraft were plotted over the Thames river estuary the undertaking was used as an exercise. It went badly wrong, however, for three military personnel were killed and seven civilians were wounded.

Some 1,700 balloons were released by Squadron Leader T. R. Poppy’s No. 2 Mobile Squadron at Herne Bay. The balloon personnel were confident that it had gone well, but it was the high degree of secrecy associated with 'Petard' which caused most of the night’s problems. When the balloons were launched, the wind direction was was as specified, but it seemed that many of the balloons failed to float at the altitude desired and then started to descend back toward the ground. Despite the fact that there had been previous 'Petard' launches, a nearby army unit was wholly unaware of this weapon, and on seeing cream-coloured balloons, with a diameter of 5 ft (1.52 m), in the moonlight, assumed that they were German weapons and opened fire on them, in many cases with tracer rounds. Many of the balloons which did not catch fire started to leak, and came down to earth over a wide area of Minster. Other leaking balloons failed to gain any great height and as the quick match fuse was burning the spool of wire began to unravel at a much lower altitude than had been anticipated. Many of the weapons fouled on the high ground around the village, shorting high-tension cables and catching on trees and hedges.

It was thought that some 200 balloons came down in the Minster area. An air raid precautions warden driving around in his car on duty ran into one of the wires and got out to remove it, but this caused the bomb to go off, and the man died from his injuries during the following day. Four balloons landed at At Eastchurch station and, not knowing what they were, some of the base’s personnel decided to collect them, believing that they were probably weather balloons. Four of the balloons were heaped in the guardroom. The disarming of the bombs was a tricky task, and the bomb disposal team, led by a Squadron Leader Dinwoodie, could see that they were in a very sensitive and dangerous state. The disarmament took several hours.

One civilian who found a balloon in a field decided to shift it to a 'safe place', and the balloon and bomb were placed on the ground next to the main railway line and covered with a sack. The bomb disposal crew had a difficult task in dealing with it as the self-destruct device was on the point of functioning.

Leaving for work at 05.00 on 1 May, a policeman from Eastchurch spotted some 50 devices hung up in trees, over hedges and across telephone lines, and as he went to work he saw many more lying about the area.

Private J. Pullen, a military policeman, was killed when a bomb exploded, and the following court of inquiry was told by another military policeman that Pilot Officer Hulbert of No. 1 Mobile Squadron had informed the two men between 23.00 and 24.00 on 31 March that the explosive charge attached to the balloon was timed to go off within one hour. It is possible that Pullen was killed because he thought the devices would have been safe after an hour as a result of the activation of the self-destruct device.

Two other men who were killed were Lieutenant J. P. Walton of the Royal Engineers, who had already received the George Medal, and Lance Sergeant C. F. Bristow, andother George Medal recipient, of the 22^nd Bomb Disposal Company, Royal Engineers. Sergeant Auten of the Royal Engineers was injured while working on bomb disposal with the Free Barrage Balloon units.

The dangerous legacy continued, however, and on 5 May, at Scapsgate, a 'Petard' device was washed ashore, and one boy was killed and another seriously injured when they tried to remove the sand bags used for altitude control.

As a result it was finally agreed to produce leaflets describing the nature of and dangers inherent in these devices, and to ensure that the public was made more aware of the 'Petard' device.