This is a B-52, most probably the D or E model from the tail design.

The original B-52 was introduced on August 5th, 1954 and has been in the USAF inventory as a nuclear delivery platform during the Cold war, and a heavy bomber during Vietnam. Although over 60 years old, the B-52 has been modified from A to H stages of development. Upgrades are still being applied to the B-52H.

The B-52H, known as "Buff" to its crews, is projected to be a staple in the inventory for the next 10 years. There are currently 65 aircraft on active duty, with 11 in reserve.

The B-52H deployed to the Middle East in early 2016, delivering intense bombing support before ground assaults against ISIS.

Over 600 B-52s were dismantled and cut up at Davis Monthan AFB, in Tucson AZ in accordance with the provisions of Salt II.

The B-57 Martin Canberra was a twin engine combat bomber used extensively in Vietnam for close air support, painted black and known as a night fighter, delivering both bombs and air to ground missiles.

The B-70 Valkyrie was an experimental Mach 3 Supersonic nuclear delivery platform first introduced in 1965. Although it was state of the art, it was prone to defensive threats.

The B-21 is still in the theoretical and design stages and will replace the B-52 sometime in the mid 2020s. It will be a zig-zag shape similar to the B2, very difficult to be identified by radar, and be able to strike anywhere in the world from the United States.

More Info: en.wikipedia.org