The Merchant Marine Act is a U.S. law enacted in 1920 that aims to support and regulate the American shipping industry. It requires that goods transported between U.S. ports be carried on ships that are built, owned, and operated by American citizens. This helps maintain a strong maritime industry and ensures national security. Additionally, the act provides financial assistance and incentives for the construction and operation of U.S. vessels. It also established the U.S. Maritime Commission, which oversees the development of the merchant marine and promotes the interests of American shipping in international trade.