Complex sentence: Johnson 1985 The additional thrust refers to the reduction of engine power required to compress the airflow; the SR-71 was more fuel-efficient at higher speeds, in terms of pounds burned per nautical mile traveled.
Split into simpler sentences: Johnson 1985 The additional "thrust" refers to the reduction of engine energy required to compress the airflow. One unique characteristic of the SR-71 is that the faster it went, the more fuel-efficient it was in terms of pounds burned per nautical mile traveled.