The first governmental issued airmail stamp was issued by Italy in May 1917. It was an Italian Express issue over printed for experimental service between Rome and Turin.
The overprint reads: ESPERIMENTO POSTA AEREA / MAGGIO 1917 / TORINO-ROMA – ROMA-TORINO.
These stamps were only sold at post offices in Turin and Rome.
The pilot was Lieutenant Mario de Bernardi, flying a Pamilio PC1 biplane. On May 20, 1917, the plane took off from Turin, carrying 400 pounds of mail, and it successfully completed the 400 mile flight to Rome in four hours and eleven minutes. The return flight was scheduled for later that day, but it was delayed until May 27, 1917, due to bad weather.