The V-3 (German: Vergeltungswaffe 3, (“Vengeance Weapon 3”) was a German World War II large-caliber gun working on the multi-charge principle whereby secondary propellant charges are fired to add velocity to a projectile, built in tunnels and permanently aimed at London, England.
The Germans planned to use the weapon to bombard London from two large bunkers in the Pas-de-Calais region of northern France, but they were rendered unusable by Allied bombing raids before completion. Two similar guns were used to bombard Luxembourg from December 1944 to February 1945.
The V-3 was also known as the Hochdruckpumpe (“High Pressure Pump,” HDP for short), which was a code name intended to hide the real purpose of the project. It was also known as Fleißiges Lieschen (“Busy Lizzie”).
They detail the shelling of Luxembourg in the article.
By the time that the Ardennes offensive began on 16 December 1944, Kammler received orders from OB West (German Army Command in the West) to begin firing at the end of the month, and the first gun tube was ready for action on 30 December 1944. Two warm-up rounds were initially fired, followed by five high-explosive shells which were fired in sequence, attended by Kammler. The muzzle velocity was approximately 935 metres per second (3,070 ft/s).
The second gun tube was brought into operation on 11 January 1945 and 183 rounds in total were fired until 22 February 1945, with 44 confirmed hits in the urban area. From the 142 rounds that struck Luxembourg, total casualties were 10 dead and 35 wounded.
Per Wikipedia:
They detail the shelling of Luxembourg in the article.
I wonder if it had a chance of actually working