The earliest container ships after the Second World War were converted oil tankers, built up from surplus T2 tankers after World War II. In 1951, the first purpose-built container vessels began operating in Denmark, and between Seattle and Alaska. The first commercially successful container ship was , a T2 tanker, owned by Malcom McLean, which carried 58 metal containers between Newark, New Jersey and Houston, Texas, on its first voyage. In 1955, McLean built his company, McLean Trucking into one of the United States' biggest freighter fleets. In 1955, he purchased the small Pan Atlantic Steamship Company from Waterman Steamship and adapted its ships to carry cargo in large uniform metal containers. On April 26, 1956, the first of these rebuilt container vessels, "Ideal X", left the Port Newark in New Jersey and a new revolution in modern shipping resulted.