On 31 March 1939, the first true production Master I conducted its maiden flight. According to "Flight", the first production examples were being delivered during late July of that year. The Master had entered RAF service just prior to the start of the Second World War Eventually, 900 Mk. I and Mk. IA Masters were constructed. This total included 26 built as the "M.24 Master Fighter" which were modified to a single-seat configuration, and armed with six .303 in machine guns for use as an emergency fighter; this model never saw any combat use.