A special alpha-number serial system was assigned during World War II to some aircraft that were forced to land in Portugal and were ultimately interned and later incorporated in the Aeronáutica Militar. This system was used to six Consolidated Liberators, which were given the serials L-1 to L-6; the Lockheed Hudson, H-1 to H-3; and the Douglas C-47 Dakota (D-1).
