Given the task definition and input, reply with output. In this task, you're given a passage, further information available on a particular linked term from the statement, and a question. Your job is to generate the answer to the question by using the information provided. If there is no clear answer obtainable, output 'none'.

Passage: While in service with the Royal Air Force film unit during World War II, Clayton shot his first film, the documentary Naples is a Battlefield (1944), representing the problems in the reconstruction of Naples, the first great city liberated in World War II, ruined after Allied bombing and destruction caused by the retreating Nazis. After the war, he was second-unit director on Gordon Parry's Bond Street (1948) and production manager on Korda's An Ideal Husband (1947). Clayton married actress Christine Norden in 1947, but they divorced in 1953. In the early 1950s, Clayton became an associate producer, working on several of the John and James Woolf's Romulus Films productions, including Moulin Rouge (1952) and Beat the Devil (1953), both directed by John Huston. It was during the making of Moulin Rouge that Clayton met his second wife, French actress Katherine Kath (born Lilly Faess), who portrayed legendary can-can dancer "La Goulue" in the film; they married in 1953, following Clayton's divorce from Norden, but the marriage was short-lived. It was also during this period that Clayton first met rising British star Laurence Harvey, with whom he worked on both The Good Die Young (1954) and I Am a Camera (1955).
Link Information: none Question: How many active aircraft does the military force that Clayton shot his first film while in service of the film unit?
Answer: none