SS Great Britain is a historic passenger steamship. She was designed by Isambard Kingdom Brunel for the Great Western Steamship Company's transatlantic service between Bristol and New York. While other ships had been built of iron or equipped with a screw propeller, Great Britain was the first to combine these features in a large ocean-going ship. When launched in 1843, Great Britain was by far the largest vessel afloat. She was the longest passenger ship in the world from 1845 to 1854. She was the first iron steamer to cross the Atlantic, which she did in 1845, in the time of 14 days. Now back in the Bristol dry dock where she was built, she serves as a museum and tourist attraction with 150,000–170,000 visitors annually.