Complex sentence: The choice of 128 mm was made because of the availability of tooling due to the use of this caliber on naval weapons, design contracts being awarded to Rheinmetall Borsig and Krupp, the first prototype guns were delivered for testing in late 1944.
Split into simpler sentences: The choice of 128 mm was made because of the availability of tooling due to the use of this caliber for naval weapons. The first prototype guns were delivered for testing in late 1944.