Complex sentence: From 1949 onwards the Band I VHF 405-line BBC transmitter network grew quickly, and in 1955 with the advent of ITV a parallel effort to provide a Band III network was also underway.
Split into simpler sentences: From 1949 onwards the Band I VHF 405-line BBC transmitter network grew quickly. In 1955 with the advent of ITV a parallel effort to provide a Band III network was also underway.