V-3 cannon

The V-3 — Vergeltungswaffe 3, "Vengeance Weapon 3" — was a multi-charge gun: secondary charges spaced along the barrel fired in turn as the shell passed them, adding velocity. It was also known as the Hochdruckpumpe, "High Pressure Pump", a code name to hide its purpose, and the symmetrical pairs of boosters along the barrel earned it the nickname Tausendfüßler, "millipede". The design was taken up in 1942 by August Coenders, chief engineer of the Röchling steelworks at Wetzlar, who proposed electrically fired charges to cure the premature ignition that had wrecked an American attempt in 1880.

Hermann Röchling put to Albert Speer a cannon capable of firing on London from the Pas-de-Calais coast: two batteries pouring hundreds of 140 kg shells an hour into the city. Speer took the proposal to Hitler in May 1943, and after the RAF bombed the Peenemünde rocket centre on 17 August, Hitler agreed that the gun be built without further tests. At Misdroy in May 1944 ranges of up to 88 km were reached, and on 4 July 1944 one of the 1.8 m shells flew 93 km before the gun burst, ending the tests.

A study in early 1943 concluded that a hill with a rock core would suit the guns best: the tubes could be sunk in inclined tunnels, or drifts, and would sit permanently laid on London. Major Bock of Festung Pioneer-Stab 27 was sent to find the ground; the choice fell on a limestone hill near Mimoyecques, in the commune of Landrethun-le-Nord, 8 km from the sea and 165 km from London. Code-named Wiese ("meadow") and Bauvorhaben 711, the works began under Organisation Todt in September 1943, and the gun shafts were excavated from October.

The plan was two parallel complexes about a kilometre apart, each with five drifts holding a stacked cluster of five gun tubes — fifty guns in all, served by an underground railway and ammunition galleries. In the eastern complex the drifts ran at 50 degrees to 105 m below the hilltop, their mouths emerging through a concrete slab 30 m wide and 5.5 m thick. German engineers and 430 miners from the Ruhr worked the site, but the bulk of the roughly 5,000-strong workforce were Russian prisoners of war, set to the work as forced labourers. A tube failure at Misdroy in April 1944, after 25 rounds, cut the site back from five drifts to three.

Bombing opened on 22 June 1944, when 98 Avro Lancasters dropped 400 tonnes on the hill. Three further raids followed with sixteen five-tonne Tallboy bombs; the last, on 6 July 1944 by RAF Bomber Command's 617 Squadron, put the site out of commission. The site never went into service. On 12 August 1944 the fortress was the target of Project Anvil: a B-24 carrying 11,000 kg of explosive was to be flown into the hill after its crew bailed out over Kent. The firing device tripped early and the aircraft exploded, killing both men aboard, one of them Joseph Patrick Kennedy Jr, elder brother of the future US president. The Germans left ahead of the Allied advance, and the 3rd Canadian Division took the site on 5 September 1944.

The project passed to the SS, and Hans Kammler ordered it into action late in 1944. Two shortened "half-barrel" guns about 50 m long were set on wooden bases in a wooded ravine of the Ruwer at Lampaden, 13 km south-east of Trier, and handed to Artillerie Abteilung 705 under Hauptmann Patzig. Their target, No. 305, was Luxembourg city, liberated that September and about 43 km off. The first tube was ready on 30 December 1944, and Kammler watched two warm-up rounds and five high-explosive shells go out; a second followed on 11 January 1945. Of 183 rounds fired up to 22 February, 142 reached Luxembourg and 44 struck within the town, killing ten people and injuring 35.

One Lampaden gun was dismantled on 15 February 1945 and firing stopped on 22 February with American units 3 km away. A second battery went up at Buhl in January 1945 to shell Belfort in support of Operation Nordwind, but was removed before it fired. All four guns were abandoned at the Röchling works in Wetzlar; the tubes, spares and remaining ammunition were captured by the US Army, tested at Aberdeen Proving Ground in Maryland, and scrapped there in 1948.

The underground galleries at Mimoyecques are open to the public as a museum, holding remains of the original ordnance, a small-scale replica of the weapon, and machinery and tools left from the works. The site carries memorials to the slave labourers the Nazis forced to build it and to the airmen killed in the attacks that destroyed it.