Excellent references on the US Merchant Marine charter, structure and history during WW2.

In the nearly 20 years following the end of the World War I, America's merchant fleet, including its cargo and passenger ships, was becoming obsolete and declining in numbers. A shipbuilding program began with the passage of the Merchant Marine Act of 1936. However, World War II provided the impetus to intensify those efforts eventually leading to a ship-building program that produced 5,500 vessels. Among them were 2,710 mass-produced ships known as Liberty ships. While reviewing blueprints of the Liberty ships at the White House, President Franklin D. Roosevelt, who loved naval vessels and had an eye for design, mused aloud to Maritime Commission administrator Admiral Emory S. Land, "I think this ship will do us very well. She'll carry a good load. She isn't much to look at, though, is she? A real ugly duckling."² Thus, the Liberty ships received their second nickname, "the ugly ducklings."

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When the United States entered World War II at the end of 1941, it had the beginnings of a great merchant fleet. But the lethal U-Boats, submarines of the German Navy, prowled the shipping lanes hunting American merchant ships. The Liberty ships proved to be too slow and too small to carry the tons of supplies the United States and her Allies would need to win the war. In 1943, the United States began a new ship-building program. These new ships would be faster, larger, and able to carry cargo long after the war was finished. These were the Victory ships.

The Liberty and Victory ships fulfilled President Roosevelt's prophetic words, serving the nation well in war and peace. Today, of the thousands of Liberty ships and Victory ships built during World War II, only a handful remain.