In May 1943 Albert Speer, the Reich's Minister of Armaments and War Production, informed Adolf Hitler of work that was being carried out to produce a large-calibre gun capable of firing hundreds of shells an hour over long distances.
The newly designed gun, codenamed the Hochdruckpumpe ("High Pressure Pump", HDP for short) and later designated as the V-3, was one of the V-weapons – Vergeltungswaffen ("retaliation or vengeance weapons") – developed by Nazi Germany in the later stages of the war to attack Allied targets.

Long-range guns were not a new development, but the high-pressure detonations used to fire shells from previous such weapons, including the Paris gun, rapidly wore out their barrels.

In 1942, August Coenders, inspired by previous designs of multi-chamber guns, suggested that the gradual acceleration of the shell by a series of small charges spread over the length of the barrel might be the solution to the problem of designing very long-range guns.
Coenders proposed the use of electrically activated charges to eliminate the problem of the premature ignition of the subsidiary charges experienced by previous multi-chamber guns.

The HDP would have a smooth barrel over 100 metres (330 ft) long, along which a 97-kilogram (214 lb) finned shell (known as the Sprenggranate 4481) would be accelerated by numerous small low-pressure detonations from charges in branches off the barrel, each fired electrically in sequence.
Each barrel would be 15 cm (5.9 in) in diameter.

The gun was still in its prototype stages, but Hitler was an enthusiastic supporter of the idea and ordered that maximum support be given to its development and deployment.
In August 1943 he approved the construction of a battery of HDP guns in France to supplement the planned V-1 and V-2 missile campaigns against London and the south-east of England.
Speer noted afterwards:
On my suggestion, the Führer has decided that the risk must be stood to award contracts at once for the "high-pressure pump," without waiting for the results of firing trials.
Maximum support is to be accorded to the experimental ranges at Hillersleben and Misdroy, and especially to the completion of the actual battery.

To reach England, the weapon needed barrels 127 metres (417 ft) long, so it could not be moved; it would have to be deployed from a fixed site.
A study carried out in early 1943 had shown that the optimal location for its deployment would be within a hill with a rock core into which inclined drifts could be tunneled to support the barrels.

The site was identified by a fortification expert, Major Bock of the Festungs-Pionier-Stab 27 of the Fifteenth Army LVII Corps based in the Dieppe area.
A limestone hill near the hamlet of Mimoyecques, 158 metres (518 ft) high and 165 kilometres (103 mi) from London, was chosen to house the gun.
It had been selected with care; the hill in which the facility was built is primarily chalk with very little topsoil cover, and the chalk layer extends several hundred metres below the surface, providing a deep but easily tunnelled rock layer.
The chalk is easy to excavate and strong enough to dig tunnels without using timber supports.
Although the site's road links were poor, it was only a few kilometres west of the main railway line between Calais and Boulogne-sur-Mer.

The area was already heavily militarised; as well as the fortifications of the Atlantic Wall on the cliffs of Cap Gris Nez to the northwest, there was a firing base for at least one conventional Krupp K5 railway gun about 5 kilometres (3.1 mi) to the south in the nearby quarries of Hidrequent-Rinxent.
In May 1943 Albert Speer, the Reich's Minister of Armaments and War Production, informed Adolf Hitler of work that was being carried out to produce a large-calibre gun capable of firing hundreds of shells an hour over long distances. The newly designed gun, codenamed the Hochdruckpumpe ("High Pressure Pump", HDP for short) and later designated as the V-3, was one of the V-weapons – Vergeltungswaffen ("retaliation or vengeance weapons") – developed by Nazi Germany in the later stages of the war to attack Allied targets.
Long-range guns were not a new development, but the high-pressure detonations used to fire shells from previous such weapons, including the Paris gun, rapidly wore out their barrels.
In 1942, August Coenders, inspired by previous designs of multi-chamber guns, suggested that the gradual acceleration of the shell by a series of small charges spread over the length of the barrel might be the solution to the problem of designing very long-range guns. Coenders proposed the use of electrically activated charges to eliminate the problem of the premature ignition of the subsidiary charges experienced by previous multi-chamber guns.
The HDP would have a smooth barrel over 100 metres (330 ft) long, along which a 97-kilogram (214 lb) finned shell (known as the Sprenggranate 4481) would be accelerated by numerous small low-pressure detonations from charges in branches off the barrel, each fired electrically in sequence. Each barrel would be 15 cm (5.9 in) in diameter.
The gun was still in its prototype stages, but Hitler was an enthusiastic supporter of the idea and ordered that maximum support be given to its development and deployment. In August 1943 he approved the construction of a battery of HDP guns in France to supplement the planned V-1 and V-2 missile campaigns against London and the south-east of England. Speer noted afterwards:
On my suggestion, the Führer has decided that the risk must be stood to award contracts at once for the "high-pressure pump," without waiting for the results of firing trials. Maximum support is to be accorded to the experimental ranges at Hillersleben and Misdroy, and especially to the completion of the actual battery.
To reach England, the weapon needed barrels 127 metres (417 ft) long, so it could not be moved; it would have to be deployed from a fixed site. A study carried out in early 1943 had shown that the optimal location for its deployment would be within a hill with a rock core into which inclined drifts could be tunneled to support the barrels.
The site was identified by a fortification expert, Major Bock of the Festungs-Pionier-Stab 27 of the Fifteenth Army LVII Corps based in the Dieppe area. A limestone hill near the hamlet of Mimoyecques, 158 metres (518 ft) high and 165 kilometres (103 mi) from London, was chosen to house the gun. It had been selected with care; the hill in which the facility was built is primarily chalk with very little topsoil cover, and the chalk layer extends several hundred metres below the surface, providing a deep but easily tunnelled rock layer. The chalk is easy to excavate and strong enough to dig tunnels without using timber supports. Although the site's road links were poor, it was only a few kilometres west of the main railway line between Calais and Boulogne-sur-Mer.
The area was already heavily militarised; as well as the fortifications of the Atlantic Wall on the cliffs of Cap Gris Nez to the northwest, there was a firing base for at least one conventional Krupp K5 railway gun about 5 kilometres (3.1 mi) to the south in the nearby quarries of Hidrequent-Rinxent.
Fortress of Mimoyecques