Complex sentence: The "U- 3" class consisted of two U-boats, "U- 3" and "U- 4", and was also a part of the Austro-Hungarian Navy's efforts to competitively evaluate three foreign submarine designs.
Split into simpler sentences: The "U- 3" class consisted of two U-boats "U- 3" and "U- 4". The class was a part of the Austro-Hungarian Navy's efforts to competitively evaluate three foreign submarine designs.