One of the most famous and successful destroyer classes ever built was the U.S. Navy's Fletcher class that appeared during the World War period. A total of 175 sister ships proved to be the largest number for a destroyer class in the U.S. Navy inventory during the era. They were completed in two and a half years, showing a stunning example of wartime mass production. Development of the Fletcher class vessels began in mid-October 1939, when the U.S. The Navy General Board stated the initial characteristics and requirements for their new destroyers. The Navy needed a larger and more versatile multipurpose destroyer to replace the then-principal Benson/Livermore Tyoe ships, which were the final development of the pre-war destroyer design restricted by the London Treaty.