During World War II, M&Ms were exclusively sold to the U.S. military.
In March of 1941, Mars was granted a patent for his manufacturing process and production began in Newark, New Jersey. Originally sold in cardboard tubes, M&Ms were covered with a brown, red, orange, yellow, green or violet coating. After the U.S. entered the war, the candies were exclusively sold to the military, enabling the heat-resistant and easy-to-transport chocolate to be included in American soldiers’ rations. By the time the war was over and GIs returned home, they were hooked.
M&Ms didn't have their signature "M" stamp until 1950.
Shortly after wartime quotas ended and the candies were made available to the general public, Forrest Mars bought out Murrie’s shares in the company and took sole ownership of the M&M brand. The familiar brown bag package that remains in use today was introduced in 1948. Two years later, the candies began to be imprinted with a black “m” (which changed to white in 1954), and customers were encouraged to “Look for the M on every piece” to ensure they were getting the real thing.
Between 1976 and 1987, there were no red M&Ms.
In the early 1970s, a bombshell Russian study was released linking FD&C Red No. 2—then the most widely used commercial food dye in America—to cancer and fetal death. Following more studies, the Food and Drug Administration banned its use in 1976. Although the red food coloring in question was not actually used in M&Ms, Mars removed red candies from the color mix to avoid consumer confusion. Following public demand, they were re-introduced in 1987—by which time Red Dye No. 2 was proven not to be carcinogenic, after all.
M&Ms were the first candy to go to space.