At Rutter's, as everywhere, the war effort was the first priority. Seventeen of the Dairy's employees went off to the service. Gas was rationed, tires were a precious commodity, and new trucks were non-existent. Maintaining a business dependent on home delivery required all sorts of ingenuity just to keep trucks on their routes. Lehman Crist recalled buying two used cars just for the tires. Nevertheless, the drivers managed to keep up their deliveries, sometimes covering two routes in one day.

The Dairy continued to prosper. By 1946, 12,000 quarts of milk were produced each day. In 1947 a quart of homogenized milk sold for 42 cents.

The 1940s also saw the first member of the second generation join the company. Dale Crist, Lehman's son, began working at the Dairy after school in 1943. During the 1940s Rutter's opened its first Ice Cream Parlor and in 1949 the company incorporated.