The M14 was developed from a long line of experimental weapons based upon the M1 Garand rifle. Although the M1 was among the most advanced infantry rifles of the late 1930s, it was not an ideal weapon. Modifications were already beginning to be made to the basic M1 rifle's design during the last months of World War II. Changes included adding fully automatic firing capability and replacing the eight-round en bloc clips with a detachable box magazine holding 20 rounds. Winchester, Remington, and Springfield Armory's own John Garand offered different conversions. Garand's design, the T20, was the most popular, and T20 prototypes served as the basis for a number of Springfield test rifles from 1945 through the early 1950s.