I knew a few BA types who were involved via phon con from seattle and the events leading up to that near fiasco. The B52 was designed for high altitude flight and generally lower aero loads at various speeds. But the militay brass had decided in that era that low level penetration was a new necessary requirement. Boeing tried to tell them No way- high speed lo level would exceed previously agreed on margins and structural loads. IOW dont do it !. My memory may be faulty- but I think the AF wanted an AF flight crew to do some low level high speed passes cuz Boeing refused to do such. I " think- I remember" that one AF crew was lost BEFORE the flight test depicted. Sure enough- the tail came off.. and crashed
And in later years, Navy TACMO wanted a 707 to do a tight turn bank to drop a near vertical low freq antenna for sub communication- and guess what- a similar event happened- and plane did land safely with no doubt brown stains on seat cushions.
Major mods to vertical sxtab resulted in both cases.