1933, AUG 12, Airmail cover to Argyll, Scotland, franked with block of six First Issue 1 A/3 p. mauve (Mi. and SG No. 5) tied by BAHRAIN cds (Donaldson type 6).
Michel and SG note Thursday Aug 10, 1933 as issuing day. This cover is presumably the earliest usage of a Bahrain overprint stamp.