During World War II hemp made a brief comeback as an American crop due to shortages of rope-making stock from other countries. Hemp for Victory is a 1942 US Department of Agriculture film that encourages farmers to grow hemp. It opens with a discussion of the ancient history of hemp (canvas derives from cannabis) and then moves into how it is being farmed in Kentucky and other US states to help in the war effort.
The film has an interesting history. For decades the USDA and the Library of Congress denied that such a thing had ever been made but in 1976 Rastafarians delivered a copy to a reporter in Florida.