When Boeing switched over from the B-52F to the B-52G in 1959, they (among other changes) lopped off the top 2.4 meters (8 feet) of the aircraft's vertical tail:
Original-height tail (here on a B-52F)
(Image by the United States Air Force, via David Legrand at Wikimedia Commons, edited by Denniss, Hohum, and Ralf Roletschek at Wikimedia Commons.)
Pruned tail (here on a B-52H)
Why did they chop off the tip of the vertical tail, thereby decreasing the aircraft's directional stability and rudder authority?