Military chocolate has been a part of standard United States military rations since the original D-ration bar of 1937. Today, military chocolate is issued to troops as part of basic field rations and sundry packs. Chocolate rations served two purposes: as a morale boost, and as a high-energy, pocket-sized emergency ration. Military chocolate rations are often made in special lots to military specifications for weight, size, and endurance. The majority of chocolate issued to US military personnel is produced by The Hershey Company.

When provided as a morale boost or care package, military chocolate is often no different from normal store-bought bars in taste and composition. However, they are frequently packaged or molded differently. The World War II K ration issued in temperate climates sometimes included a bar of Hershey's commercial-formula sweet chocolate. But instead of being the typical flat thin bar, the K ration chocolate was a thick rectangular bar that was square at each end. (In tropical regions, the K ration used Hershey's Tropical Bar formula.)

When provided as an emergency field ration, military chocolate was very different from normal bars. Since its intended use was as an emergency food source, it was formulated so that it would not be a tempting treat that troops might consume before they needed it. Even as attempts to improve the flavor were made, the heat-resistant chocolate bars never received enthusiastic reviews. Emergency ration chocolate bars were made to be high in energy value, easy to carry, and able to withstand high temperatures. Withstanding high temperatures was critical since infantrymen would often be outdoors, sometimes in tropical or desert conditions, with the bars located close to their bodies. These conditions would cause typical chocolate bars to melt within minutes.

The first chocolate ration bar commissioned by the United States Army was the Field Ration D or Ration, Type D, commonly known as the "D ration." Army Quartermaster Colonel Paul Logan approached Hershey's Chocolate in April 1937, and met with William Murrie, the company president, and Sam Hinkle, the chief chemist. Milton Hershey was interested in the project when he was informed of the proposal, and the meeting began the first experimental production of the D ration bar.

Colonel Logan had four requirements for the D ration bar, dictating that it had to:

Its ingredients were chocolate, sugar, oatmeal, cacao fat, skim milk powder, and artificial flavoring, fortified with vitamin B1 to prevent beriberi. Chocolate manufacturing equipment was assembled to move the flowing mixture of liquid chocolate and oat flour into preset molds. However, it was found that the temperature-resistant formula became a gooey paste that would not flow at any temperature. Hinkle was forced to develop entirely new production methods to produce the bars. Each four-ounce portion had to be kneaded, weighed, and pressed into a mold by hand. The end result was an extremely hard block of dark brown chocolate that would crumble with some effort and was heat-resistant to 120 °F (49 °C). The resultant bar was wrapped in aluminum foil and placed in a cardboard carton. Three bars made up a daily ration and was intended to furnish the individual combat soldier with the 1,800 calories (7,500 kJ) minimum sustenance recommended each day.

Logan was pleased with the first small batch of samples. In June 1937, the United States Army ordered 90,000 "Logan Bars" and field tested them at bases in the Philippines, Panama, on the Texas border, and at other bases throughout the United States. Some of the bars even found their way into the supplies for Admiral Richard E. Byrd's third Antarctic expedition. These field tests were successful, and the Army began making irregular orders for the bars. After the attack on Pearl Harbor, the bars were ordered to be packaged to make them poison gas-proof. The bars' boxes were covered with an anti-gas coating and were packed 12 to a cardboard carton, which was also coated. These cartons were packed 12 to a wooden crate, for a total of 144 bars to a crate.

After US entry into the Second World War, Congress planned to shut down the candy industry for the duration of the conflict, deeming it non-essential. Milton Hershey, fighting off attempts to ration sugar, corn syrup, and cocoa, claimed to Congress that chocolate was a vital source of nutrition for the nation's troops. During the war years, the bulk of the Hershey Food Corporation's chocolate production was for the military. Between 1940 and 1945, an estimated three billion units of the specially formulated candy bars were distributed to soldiers around the world."