Complex sentence: The RAF lacked aircraft large enough to transport Chinooks and so the helicopter crews flew themselves to Freetown, and the flight undertaken by the two UK-based aircraft became the longest self-deployment of helicopters in British history.
Split into simpler sentences: The RAF lacked aircraft large enough to transport Chinooks and so the helicopter crews flew themselves to Freetown. The flight undertaken by the two UK-based aircraft was the longest self-deployment of helicopters in British history.