Passage: Production drawings were completed in 1960 allowing construction of prototypes to begin, but the political climate in China resulted in the project being canceled in 1961. A small team kept the program alive until it work restarted in earnest at Nanchang. The first flight finally occurred on 10 June 1965. Series production began in 1969, with squadron delivery starting in 1970.

Question: When did the squadron delivery start?
1970