The United States Maritime Commission was an independent executive agency of the U.S. federal government that was created by the Merchant Marine Act of 1936, passed by Congress on June 29, 1936, and replaced the United States Shipping Board which had existed since World War I. It was intended to formulate a merchant shipbuilding program to design and build five hundred modern merchant cargo ships to replace the World War I vintage vessels that comprised the bulk of the United States Merchant Marine, and to administer a subsidy system authorized by the Act to offset the cost differential between building in the U.S. and operating ships under the American flag. It also formed the United States Maritime Service for the training of seagoing ship's officers to man the new fleet.