An Allied bombing raid (during which Joseph Kennedy, elder brother of future president John F. Kennedy, died along with the rest of the crew of the Liberator bomber he commanded) destroyed the Mimoyecques facility on July 16th, 1944.
The project to bomb London using the V-3 was thus scrapped, but tests with shorter-barreled versions were continued under SS-Gruppenführer Hans Kammler. He ordered the project to be intensified to be ready for action in late fall 1944.
Two 150 mm caliber versions with 12 pairs of side chambers at 90° and a barrel length of some 50 meters were constructed some 43 km east of Luxembourg (the city). These were subordinated to the 550 man strong Heeres Artillerie Abteilung (army artillery unit) 705 under Hauptmann Patzig.
The shorter V-3's were almost complete by the time the Germans started their offensive in the Ardennes, but procuring proper ammunition for the guns was difficult due to the disrupted railway lines. It was decided to use high explosive charges from various available ammunition, amounting to 7-9 kg of payload for each 95-kg shell. The initial propellant charge was 5 kg, and the secondary charges totalled 68 kg.
Luxembourg was their designated target. The shelling started on December 30th, 1944. Between this date and February 22nd, 1945, when the advancing Allied forces made further operations impossible, the two V-3's fired a total of 183 projectiles at Luxembourg, with 143 hitting the city.
The V-3 shelling of Luxembourg claimed a total of 10 (civilian) lives and wounded 35.
Source:
http://www.nat-military-museum.lu/pageshtml/museumspecial.html