Complex sentence: It is unknown when, if, or how many of No 29 Squadron's Blenheim aircraft were fitted with them in 1940 as the squadron continued to practice, and struggle with, adapting to night-fighter tactics.
Split into simpler sentences: It is unknown when, if, or how many of No 29 Squadron's Blenheim aircraft were fitted with them in 1940. The squadron continued to practice, and struggle with, adapting to night-fighter tactics.