Complex sentence: The Keystone LB-6 and LB-7 were 1920s American light bombers, built by the Keystone Aircraft company for the United States Army Air Corps, called Panther by the company, but adoption of the name was rejected by the U.S. Army.
Split into simpler sentences: The Keystone LB-6 and its sister LB-7 were a 1920s American light bomber built by the Keystone Aircraft company for the United States Army Air Corps. It was called the Panther by the company but adoption of the name was rejected by the U.S. Army.