When did the American military begin using metric measurements? Random sampling of Google search results for "U.S. military metric system" indicates it's often used when dealing with joint maneuvers with allied nations that use metric, and I'm pretty sure I've run into kilometers and meters—distance units—in my reading. I found out from dear ol' Wikipedia that the U.S. was a signatory to the original convention establishing the metric system as a world standard, but the closest to a date I found for military use was all the way into the 1970s.
Essentially I need to know if my men could refer to distance in kilometers in World War II fiction. I think they can but I'd like to be sure.