# What is the historical reasons to start Belgians registrations with "OO-"?

For many countries, the registration number begins with a obvious letter (F for France, D for German (Deutschland I guess), C for Canada,...). For other, historical reasons have already been covered here (e.g. Where did the US 'N' registration letter come from?).

But for Belgium, I find it weird to begin with OO. Is there an historical reason for that? if so, what is it?

• D is for Djermany. Just say it aloud and suddenly it makes sense. ;-) Apr 18 '20 at 8:14
• And G for UK-registered aircraft (for some reason), EI for Ireland (Eire), RA for Russia, JA for Japan, I for Italy, UR for the Ukraine, CU for Cuba, YU for Serbia (formerly Yugoslavia), LX for Luxembourg, Z for Zimbabwe... Apr 18 '20 at 17:34