Well, that was easier than I thought it'd be. I knew:

During 1943, U.S. officials imposed a short-lived ban on sliced bread as a wartime conservation measure.[10][11] The ban was ordered by Secretary of Agriculture Claude R. Wickard, who held the position of Food Administrator, and took effect on January 18, 1943. According to The New York Times, officials explained that "the ready-sliced loaf must have a heavier wrapping than an unsliced one if it is not to dry out." It was also intended to counteract a rise in the price of bread, caused by the Office of Price Administration's authorization of a ten percent increase in flour prices.

So guessed it might be a '40's thing. Normally bread needs a sawing action (at least in my experience) to slice and I didn't see any such provision. Being wood I didn't think it was for meat, so gave up and asked the experts. Thanks so much.