Complex sentence: Boeing developed the aircraft as a private venture to replace the Boeing F3B and Boeing F2B with the United States Navy that was the first flight of the P-12 took place on 25 June 1928.
Split into simpler sentences: Boeing developed the aircraft as a private venture to replace the Boeing F3B and Boeing F2B with the United States Navy. The first flight of the P-12 took place on 25 June 1928.