Complex sentence: By September 1943 all of the Whitleys had been take out of active service at Chivenor, and four squadrons of Wellingtons, 172,407,612 and 304, were located at the base.
Split into simpler sentences: By September 1943 all of the Whitley had been take out of active service at Chivenor. Four squadrons of Wellingtons 172,407,612 and 304 were located at the base.