Progress is fine, but it's gone on for too long.: The Thud

The World Book Encyclopedia. Chicago: Field Enterprises Educational Corporation, 1971.

The "Thud" was the workhorse of the American bomber force flying over North Vietnam. For an excellent account of what it was like to fly this animal in combat, read Colonel Jack Broughton's 1969 book, Thud Ridge (Bantam, 1985).