Liberty ships were mass-produced during World War II. They were freighters with a simple design that made them quick and easy to build. The number of decks on freighters gradually increased the speed and flexibility of loading. A freighter is a cargo vessel primarily engaged in carrying general merchandise. They normally have large, unobstructed cargo holds with overall capacities of 10,000 deadweight tons. Today's freighters may have capacities up to 14,000 deadweight tons, and may be adapted to carry containers.