Complex sentence: The first three missions, overland from Greece, were trouble free and larger numbers were landed by sea and air under Operation Valuable which continued until 1951, increasingly under the influence of the newly formed CIA.
Split into simpler sentences: The first three missions, overland from Greece, were trouble-free. Larger numbers were landed by sea and air under Operation Valuable, which continued until 1951, increasingly under the influence of the newly-formed CIA.