Complex sentence: The Sikorsky HLH was a proposed aircraft design to meet the United States Army requirement in 1970 for a Heavy Lift Helicopter capable of carrying, a lifting capacity about twice that of any existing domestic helicopter.
Split into simpler sentences: The Sikorsky HLH was a proposed aircraft design to meet a United States Army requirement for a Heavy Lift Helicopter capable of carrying. In 1970 the U.S. Army expressed a need for a helicopter with a lifting capacity about twice that of any existing domestic helicopter.