I'm curious - how many countries used metric measures for instrumentation? I think its altitude and speed measures that are the most important, as Lusche pointed out distance is not changed much by using yards vs meters.
RAF - English measure
USN, AAF - English measure
Luftwaffe - Metric system
Soviet - ? Metric?
Japanese - ? I could see this going either way as I think before the War the British traded with Japan militarily (sold them naval vessels) and Japanese radials started as licensed copies of U.S. radial engines, I think.