Complex sentence: In the weeks following the invasion, Polish forces and contingents from Belgium, Czechoslovakia, Greece and the Netherlands participated, most also provided air and naval support, as did the Royal Australian Air Force, the Royal New Zealand Air Force and the Royal Norwegian Navy.
Split into simpler sentences: In the weeks following the invasion, Polish forces also participated, as well as contingents from Belgium, Czechoslovakia, Greece, and the Netherlands. Most of the above countries also provided air and naval support, as did the Royal Australian Air Force, the Royal New Zealand Air Force, and the Royal Norwegian Navy.