On May 15, 1942, 17 states joined up to begin rationing gasoline as part of the United States’ World War II effort. It was mostly Eastern states that had done so, but by the end of the year, all 48 states were required to join the ration.

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After the bombing of Pearl Harbor on December 7, 1941, the US finally committed to joining World War II by declaring war against Japan, with Germany and Italy subsequently declaring war on America. For a country that had avoided choosing sides or sending men into battle, the shift on the home front was massive. Enlisted men were shipped off to war, and women hit the factories. Automotive plants bgan making tanks and planes. Households had to limit the consumption of products like rubber, sugar, alcohol, and cigarettes.

But gasoline was just as important for the war effort, since something needed to be used to power all those planes. Here’s a little more from :

Ration stamps for gasoline were issued by local boards and pasted to the windshield of a family or individual’s automobile. The type of stamp determined the gasoline allotment for that automobile. Black stamps, for example, signified non-essential travel and mandated no more than three gallons per week, while red stamps were for workers who needed more gas, including policemen and mail carriers. As a result of the restrictions, gasoline became a hot commodity on the black market, while legal measures of conserving gas—such as carpooling—also flourished. In a separate attempt to reduce gas consumption, the government passed a mandatory wartime speed limit of 35 mph, known as the “Victory Speed.”

There were various levels of stamps that were issued based on how important you were. Families and average motorists got an “A” sticker on their windshield. Folks with jobs where transportation was necessary or who had crucial jobs like doctors received “B,” “C,” “T,” or “X” depending on their level of importance.