A: Because they melted in your mouth, not in your hand.
Melting chocolate was not a trivial issue for a soldier who might have to put down his candy bar and pick up a gun.
Frank Mars began making candy in his kitchen in Tacoma, Washington, in 1911; in 1923 he developed the Milky Way bar, which quickly became a nationally known brand in an era when national brands were in many areas edging out locally made products. In the next two decades the Mars company further extended their national reach with Snickers and 3Musketeers. In 1932 they went international when Frank’s son Forrest moved to England to set up a candy business (and expanded into pet foods). When the war broke out Forrest returned to the United States and established M&M Limited in Newark, taking the name from his initial and that of executive Bruce Murrie. Further seeking to extend their market, they came up with M&Ms as a way of dealing with the falloff in candy sales over the summer, when consumers stopped buying chocolate and stores stopped stocking chocolate because, in an era before widespread air-conditioning, it had a tendency to turn into a gooey mess.
But the real success of M&Ms apparently came when it was issued as part of U.S. service personnel rations because its hard outer shell made of sugar prevented it from melting before being eaten. Soldiers came home eating M&Ms, and its particular appropriateness to all climates was encapsulated in the slogan (coined in 1954): “The milk chocolate melts in your mouth—not in your hand.”
M&Ms were not the only chocolate issued to soldiers. The Hershey company, at the request of the army, developed a chocolate ration that would sustain a soldier who had nothing else to eat and could be carried in his pocket unmelted. Throughout the war, Hershey turned out a half million bars a day of “Ration D,” a 4-ounce, 600-calorie chocolate bar.
Regular chocolate bars were also available at the PX, where they were the second most popular item after cigarettes. When American troops invaded Europe, the chocolate bar became closely associated with American GIs, who turned chocolate into the all-purpose medium of exchange that could be bartered for local antiques or even sexual favors.
The first change in the mix of M&M colors came in 1995 when blue replaced tan. In case you were wondering, an average batch of plain M&Ms is 30 percent browns, 20 percent each of yellows and reds, and 10 percent each of greens, oranges, and blues.
Sources: Marcia and Frederic Morton, Chocolate: An Illustrated History (1986); A Little Encyclopedia of M&M/Mars (1995); Ron Lees, A History of Sweet and Chocolate Manufacture (1988); “Candy and the War,” Newsweek, June 14, 1943, p. 77; Washington Post, September 11, 1995.