NM in this instance is probably Nautical Miles as opposed to Nano Meters
The abbreviation for nanometers is lowercase nm, capital NM would be for nautical miles. It's particularly important to remember that whether something is uppercase or lowercase can greatly impact the unit of measurement, even within the same system of measurement. For example Pm equals petameters (10^15), but pm equals picometers (10^-12).
Markings based on Boeing F-13A-5-BN (converted for photo-reconnaissance from B-29A-5-BN) s/n 42-93852 c/n 7259 "Tokyo Rose", which on 1 Nov 1944 became the first US aircraft to overfly Tokyo since the 1942 Doolittle raids.
"This is Radio Tokyo, and this is the song "Zero Hour" performed by the Idol of the fleet, Naka-chaaaaaan!"The Floating Fortress en route to Tokyo for information gathering task, while undergoing intense signal jamming.
(Location: 100 nautical miles South of Tokyo)
