During WWII, mail, invaluable to the morale of American troops overseas, took up valuable cargo space. In June 1942, the U.S. Postal Service developed a 7 x 9 1/8″ paper and envelope Vmail form. Letters written on the standardized form were first censored, then transformed into thumbnail-sized negative microfilm images. Upon arrival at their overseas destination, the negatives were enlarged to 60% of their original size and printed.
According to the Smithsonian National Postal Museum, 37 mail bags required to carry 150,000 one-page letters could be replaced by a single mail sack, reducing the weight of the mail from 2,575 to 45 pounds.