actually, water injection only slightly increased the RPM's -- almost negligibly. I was a crew chief on KC-135A's at Castle AFB back in the early 80's. On a turbojet engine, water injection cooled the inlet charge, made the air denser, & therefor had more potential for expansion. was similar in practice to hitting afterburner. depended on the ambient air temperature more than anything else as to it's effectiveness. if it was 110 degrees out, & you had a heavy fuel load, you probably wouldn't have enough runway to get off the ground without water. the new CFM56 engines made it all a moot point though, quieter, more efficient, & about twice the thrust of the old J57's. The BUFF's still use the J57's btw.