Complex sentence: The Sikorsky S-34 was a 1920s American six-seat sesqiuplane was designed and built by the Sikorsky Manufacturing Corporation, only one was built but the design led to the successful Sikorsky S-38.
Split into simpler sentences: The Sikorsky S-34 was a 1920s American six-seat sesqiuplane, designed and built by the Sikorsky Manufacturing Corporation. Only one was built but the design led to the successful Sikorsky S-38.