High Quality Content by WIKIPEDIA articles! Dunderberg, which is a Swedish word meaning "thunder(ing) mountain," was an ocean-going ironclad screw frigate of 16 guns. She was designed by Lenthall as a reproduction of CSS Virginia, with two 21-foot screws, sloping armored casemate sides, and a 50-foot ram. She had a double bottom and collision bulkheads, and was the longest wooden ship ever built. Her keel was laid down in October 1862 by W.H. Webb of New York City. Her construction was initially spurred by the threat of war with the United Kingdom. After that impetus abated, construction lagged, and she was not launched until 2 March 1865. The American Civil War ended before she could be completed, and was formally rejected by the U.S. Navy in September 1866.