'Wiese' was a German plan to attack London, the British capital, with the V-3 (otherwise HDP) high-technology artillery system (1944/45).

The Germans planned to use the weapon to bombard London from two large bunkers in the Pas de Calais region of north-eastern France, but these were rendered unusable by Allied bombing raids before they could be completed, but two similar guns were used to bombard Luxembourg from December 1944 to February 1945.

The V-3 was a weapon working on the multi-charge principle, and was also known as the Hochdruckpumpe (high-pressure pump, or HDP), which was a codename to hide the real purpose of the project. The weapon was also known as the Fleissiges Lieschen (busy lizzie).

The gun used multiple propellant charges in secondary chambers located along the barrel’s length and each timed to fire as soon as the projectile had passed it in order to provide an additional boost. Solid-fuel rocket boosters were used instead of conventional propellant charges because of their greater suitability and ease of use. These were arranged in symmetrical pairs along the length of the barrel, angled to project their thrust against the base of the projectile as it passed. This layout spawned the German codename 'Tausendfüssler' (millipede). The barrel and side chambers were designed as identical sections to simplify production and to facilitate the replacement of any damaged sections, and the entire weapon comprised a number of such sections bolted together. The weapon was of the smooth-bore type and fired a fin-stabilised shell which relied on aerodynamic rather than gyroscopic forces to prevent tumbling. Wholly distinct from conventional rifled weapons, this resulted in a lower drag coefficient and thus increased range.

The origin of the multi-chamber gun can be dated to 1857, and in 1918 the French planned a very long range multi-chamber gun in response to the German 'Paris Gun'. This latter had been constructed by Friedrich Krupp AG and could bombard Paris from German lines over a distance of no less than 78 miles (125 km). The French plan did not reach even the prototype stage, however, and was discontinued when the retreat of the German armies and the armistice put an end to the bombardment. The plans for the multi-chamber gun were archived, as the weapon had been envisaged specifically to counter the German long-range gun.

When France was defeated in June 1940, the Germans acquired the plans of this long-range gun, and in 1942 caught the attention of August Cönders, developer of the Röchling shell and chief engineer of the Röchling Stahlwerk A. G. Cönders thought that the gradual acceleration of the shell by the firing of 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, for the very powerful propellant charge required to give current shells a high velocity caused the very rapid degradation of the gun tubes of conventional guns.

Cönders therefore proposed the use of electrically initiated charges to eliminate the problem of the premature ignition of the subsidiary charges, a problem which had bedevilled earlier experimental weapons of this type. Cönders built a prototype of a 20-mm multi-chamber gun using machinery readily available at Röchling Stahlwerk’s factory. The first tests were encouraging but, in order to get the support of the armaments ministry, Hermann Röchling had to suggest to Albert Speer, the minister for armaments production, that Cönders' project was for a cannon capable of firing on London from the coast of the Pas de Calais. The project intended to use two batteries to crush London under a barrage of hundreds of shells per hour, each shell weighing 309 lb (140 kg) and carrying a 55-lb (25-kg) explosive charge.

Cönders built a full-calibre 5.91-in (150-mm) gun at the Hillersleben proving ground near Magdeburg but, by the end of 1943 he had run into severe problems both in putting the gun’s basic principle into practice and in creating a feasible design for the shells that it was to fire. When everything worked, though, the muzzle velocity was little moe than 3,280 ft (1000 m) per second, far short of the promised figure. Even so, it was proposed that one full-sized gun with a 492-ft (150-m) barrel be constructed at Misdroy on the Baltic island of Wolin, near Peenemünde, while construction went ahead at the Mimoyecques site in France, which had already been attacked by the USAAF and the RAF.

The Heereswaffenamt (weapon procurement office) had assumed control of the project by March 1944, when there was still no news from Misdroy about satisfactory performance, and Cönders became one of the engineers working on the three chief problems: projectile design, obturation, and ignition of the secondary charges.

Six different companies, including Krupp and �koda, produced satisfactory projectile designs. Obturation problems were solved by placing a sealing piston between the projectile and the initial propellant charge, which in turn prevented the flash from the charge from getting ahead of the projectile and solved the problem of controlling the initiation of the secondary charges. By the end of May 1944, there were four designs for the 5.91-in (150-mm) finned projectile, one designed by Füstenberg and manufactured by Fasterstoff, one by Cönders and manufactured by Röchling, one designed by Verein-Haack and manufactured by Bochumer, and one designed by Athem and manufactured by Witkowitz.

In trials at Misdroy between 20 and 24 May 1944, ranges of as much as 55 miles (88 km) were achieved. The, on 4 July of the same year the Misdroy gun test-fired eight rounds, one of the projectiles, 6 ft 11 in (1.80m) long, reached 58 miles (93 km), but the gun then burst, putting an end to the tests.

Major Bock of the 27^th Festungpioneerstab, the fortification regiment of General Walther Fischer von Weikersthal’s LXVII Corps within General Hans von Salmuth’s 15^th Army, at the time based in the Dieppe area, was given the task of finding a suitable site for the HDP batteries following Adolf Hitler’s decision that these weapons should be sited in north-eastern France to bombard London. A study in early 1943 concluded that a hill with a rock core would be most suitable, as the gun tubes could be placed in drifts (inclined tunnels) with their support equipment and supplies located in adjacent tunnels. The guns would not be movable and would be permanently aimed at London.

A suitable site was selected at a limestone hill about 3.1 miles (5 km) to the north of the Hidrequent quarries near Mimoyecques in the Pas de Calais behind Cap Gris Nez, where V-1 and V-2 launch sites were already under construction. The site was 5 miles (8 km) from the sea and 103 miles (165 km) from London, and received the codenames 'Wiese' and 'Bauvorhaben 711' (Construction Project 711), and the Organisation 'Todt' started work on the installation during September 1943 with the building of railway lines to support the work. Work on the excavation of the gun shafts began in October. The initial layout comprised two parallel facilities about 1,095 yards (1000 m) apart, each with five drifts which were to hold a stacked cluster of five HDP gun tubes, for a total of 50 guns. Both facilities were served by an underground railway tunnel and underground ammunition storage galleries.

The eastern site comprised five drifts angled at 50° and extending 345 ft (105 m) below the crest of the hill. The five drifts exited the crest through a concrete slab 32.8 yards (30 m) wide and 18 ft (5.5 m) thick. Large steel plates protected the five openings, and each drift had a special armoured door. Extensive tunnels and elevator shafts supported the guns and, if the site had become operational, about 1,000 troops of the 705^th Artillerieabteilung and supporting units would have been deployed at Mimoyecques. The 705^th Artillerieabteilung had been created in January 1944 under the command of Oberstleutnant Georg Borttscheller to operate the 'Wiese' gun complex.

The German scheme was to have the first battery of five gun tubes ready for March 1944, and the full complex of 25 gun tubes by 1 October 1944. A failure occurred, however, at the Misdroy proving ground in April 1944 after only 25 rounds had been fired and, as a result, the project was further cut back from five drifts to three, even though work had begun on some of the other drifts. The site was finally put out of commission on 6 July 1944, when Avro Lancaster heavy bombers of RAF Bomber Command’s No. 617 Squadron attacked the site with 12,000 lb (5443-kg) 'Tallboy' deep-penetration bombs.

The entire programme eventually came under the control of the SS, and SS-Obergruppenführer und General der Waffen-SS Dr-Ing. Hans Kammler ordered it to be ready for action in late 1944 with the assistance of Generalmajor Dr Walter Dornberger. Work was initiated on a battery of two shorter guns, each about 164 ft (50 m) long with 12 side chambers, and this was placed in the hands of the 705^th Artillerieabteilung under the command of Hauptmann Patzig. The guns were sited in a wooded ravine of the Ruwer river at Lampaden about 8.1 miles (13 km) to the south-east of Trier in western Germany.

Aimed to the west, the guns rested on 13 steel support structures on solid wooden bases at an elevation angle of 34°. The city of Luxembourg, which the Allies had liberated in September 1944, was about 27 miles (43 km) distant and designated as Target No. 305. Concrete blockhouses were constructed between the two gun tubes, as well as 10 smaller bunkers to hold projectiles and propellant charges.

The assembly and mounting of the Lampaden guns coincided with the Germans' final preparations for the 'Wacht am Rhein' offensive, but the delivery of ammunition became problematical as a result of the chaos pervading the German railway network. Time had become critical, and it was decided to use a 5.91-in (150-mm) finned projectile with a discarding sabot, weighing 209 lb (95 kg) and carrying between 15.4 and 19.8 lb (7 and 9 kg) of explosive. The propellant comprised an 11-lb (5-kg) main charge and 24 subsidiary charges for a total of 161 lb (73 kg).

By the time 'Wacht am Rhein' began on 16 December 1944, Kammler received orders from Generalfeldmarschall Gerd von Rundstedt, the Oberbefehlshaber 'West', to begin firing at the end of the month, and the first gun tube was ready for action on 30 December, and two warm-up rounds were followed by five HE projectiles at a muzzle velocity of about 3,068 ft (935 m) per second. The second gun was brought into service on 11 January 1945, and in all some 183 rounds were fired in the period to 22 February 1945, with 44 confirmed hits in the urban area of Luxembourg. The guns were not particularly effective: from the 142 rounds that struck Luxembourg, the total casualties were 10 dead and 35 wounded.

One of the two Lampaden guns was dismantled on 15 February,[30] and firing ceased on 22 February, when US Army units had advanced to within 1.85 miles (3 km) of Lampaden.

A second battery was deployed in January 1945 at Buhl, aimed at Belfort in support of the 'Nordwind' (iii) offensive, but only one gun had been completed before the failure of 'Nordwind' (iii) put the site at risk, and the equipment was removed before firing could begin.

There were other proposals to deploy batteries to bombard London, Paris, Antwerp and other cities, but none of these was implemented as a result of the dire state of the German railway network and a lack of ammunition. All four guns were eventually abandoned at the Röchling works in Wetzlar, and the 705^th Artillerieabteilung was re-equipped with conventional artillery. The disassembled gun tubes, spare parts, and remaining ammunition were later captured by the US Army and shipped to the USA, where they were tested and evaluated at the Aberdeen Proving Ground, Maryland, before being scrapped in 1948.