The 'Leopold' and and its twin the 'Robert' were of the 28cm K5(E) design. The Leopold had an unconfirmed range of 11 miles and fired a pre-engraved projectile weighing approximately 550 pounds. It is fired from a turntable affording a 360 degree traverse.
The Leopold is currently on display at the Aberdeen Proving Ground in Aberdeen, Maryland. The following excerpt detailing how the Leopold fell into Allied hands was taken from the Aberdeen Proving Ground brochure.
"It is hard to imagine that the Germans could conceal a weapon capable of firing a 550-pound shell. The German Leopold Gun was the largest weapon which lobbed shells at American troops at "Anzio Beach". An aura of mystery surrounded the employment of the gun. To the bewilderment of allied officials who knew the approximate location of the Leopold, the gun could not be silenced. Repeated bomber and naval attacks failed. It wasn't until the Allies broke out of the "Anzio Beachhead" and sent the Germans scurrying that the secret was revealed. The Leopold supported by 24 railcar wheels, was mounted on railroad tracks which led in and out of mountain tunnels. When not firing, the gun was rolled back into the tunnels out of the sight of Allied reconnaissance. Because bombs had destroyed Italian rail systems, the Germans were forced to leave the Leopold and its twin gun "Robert" behind. Although both guns had been extensively damaged, Allied forces were able to salvage the Leopold and after reconstruction of the railway, moved the gun to Naples for shipment to the United States. "Anzio Annie" as the gun was known to the Allied troops at Anzio, is the only German railroad gun known to have survived World War II."