Since the Belgian military had officially surrendered in May 1940 and the Belgian Constitution specifically forbade Belgians from joining foreign militaries, the Free Belgian forces were officially committing treason; the charge was only annulled in 1948 and nobody was prosecuted.[11] Despite the formation of all-Belgian ground units from late 1940, many Belgian volunteers – especially those in the Royal Air Force – served in majority British units, particularly in the early years after the formation of the Free Belgian forces.[12]