Complex sentence: Some are designed for addition of, or may include, a ski jump ramp allowing for STOVL operations or may have an unused ski jump installed before retirement of STOVL aircraft and re-purposing, in the past conventional carriers were converted and called commando carriers.
Split into simpler sentences: Some are designed for addition of, or may include, a ski jump ramp allowing for STOVL operations or may have an unused ski jump installed before retirement of STOVL aircraft and re-purposing. In the past conventional carriers were converted and called commando carriers.