The earlier models were manufactured in the 1950s. Most of the H models were manufactured in 1960 and 1961, but they have undergone significant airframe improv

The earlier models were manufactured in the 1950s. Most of the H models were manufactured in 1960 and 1961, but they have undergone significant airframe improvements, several engine improvements, and of course, avionics improvements. It's still a B-52, but it's a "B-52H Block $whatever_design_block_they_are_on_these_days" model.