Complex sentence: The first company "construction" was actually an old Raab-Katzenstein "Schwalbe Kl 1c" upgraded to "Schwalbe II", and at least one complete "Schwalbe II" was also constructed.
Split into simpler sentences: The first company "construction" was actually an old Raab-Katzenstein "Schwalbe Kl 1c" upgraded to "Schwalbe II". At least one complete "Schwalbe II" was also constructed.