The Air Force's B-1B Lancer has had problems with mission readiness this year.
The Lancer is a long-range, multi-role heavy bomber and has been in service since 1985, although its predecessor, the B-1A, was developed in the 1970s as a replacement for the B-52.
The B-1B is built by Boeing and has a payload of 90,000 pounds. The Air Force is also looking at ways to expand that payload to carry more weapons and heavier weapons, including hypersonics.
The Lancer has a wingspan of 137 feet, a ceiling of 30,000 feet, and can hit speeds up to Mach 1.2, according to the Air Force. There are 62 B-1Bs currently in service.
The B-1B was considered nuclear-capable bomber until 2007, when its ability to carry nuclear arms was disabled in accordance with the START treaty.
The B-1B is not scheduled to retire until 2036, but constant deployments to the Middle East between 2006 and 2016 "broke" the fleet.
Service officials and policymakers are now considering whether the Lancer can be kept flying missions, when it should retire, and what that means for the bomber fleet as a whole.
The B-52 bomber has been in service since 1955.
The Air Force's longest-serving bomber came into service in 1955 as the B-52A. The Air Force now flies the B-52H Stratofortress, which arrived in 1961.
It has flown missions in Iraq during Operation Desert Storm and during operations against ISIS.
The B-52H Stratofortress can carry a 70,000 pound payload, including up to 20 air-launched cruise missiles, and can fly at 650 mph. It also recently dropped laser-guided bombs for the first time in a decade.
The Stratofortress is expected to be in service through 2050, and the Air Force has several upgrades planned, including new engines, a new radar, and a new nuclear weapon.
As of June 2019, there were 58 B-52s in use with the Air Force and 18 more with the Reserve.
Two B-52s have returned to service from 309th Aerospace Maintenance and Regeneration Group (AMARG) at Davis-Monthan Air Force Base in Arizona, also known as the "boneyard," where retired or mothballed aircraft are stored.
One bomber, nicknamed "Ghost Rider" returned in 2015, and the other, "Wise Guy," in May.
"Wise Guy," a Stratofortress brought to Barksdale Air Force Bease in Louisiana to be refurbished, had a note scribbled in its cockpit, calling the aircraft, "a cold warrior that stood sentinel over America from the darkest days of the Cold War to the global fight against terror" and instructing the AMARG to "take good care of her … until we need her again."
The B-2 Spirit stealth bomber is the only stealth bomber in operation anywhere.
The B-2 was developed in a shroud of secrecy by Northrop Grumman. It is a multi-role bomber, capable of delivering both conventional and nuclear munitions.
It has a payload of 40,000 pounds and has been in operational use since 1993. July was the 30th anniversary of the B-2's first flight, and the Air Force currently has 20 of them.
The Spirit can fly at an altitude of up to 50,000 feet and has an intercontinental range.
The B-2 operates out of Whiteman Air Force Base in Missouri, and three of the bombers are currently flying out of RAF Fairford in the UK.
From Fairford, the B-2 has completed several firsts this year — the first time training with non-US F-35s, its first visit to Iceland, and its first extended flight over the Arctic.
Little is known about the B-21 Raider, the Air Force's future bomber.
What we do know: It will be a stealth aircraft capable of carrying nuclear and conventional weapons.
Built by Northrop Grumman, the B-21 is named for Doolittle's Raiders, the crews who flew a daring bomb raid on Japan just a few months after the attack on Pearl Harbor.
The Air Force said last year that B-21s would go to three bases when they start arriving in the mid-2020s: Dyess Air Force Base in Texas, Ellsworth Air Force Base in South Dakota, and Whiteman Air Force Base in Missouri.
Air Force Magazine reported in July that the B-21 could fly as soon as December 2021.
Air Force Vice Chief of Staff Gen. Stephen Wilson said on July 24 that he has an application on his phone "counting down the days … and don't hold me to it, but it's something like 863 days to first flight," according to Air Force Magazine.
The B-21 also loomed over the B-2's 30th anniversary celebrations at Northrop's facility in Palmdale, California, where the B-2 was built and first flew.
Company officials have said work on the B-2 is informing the B-21's development, and recently constructed buildings at Northrop's Site 7 are thought to be linked to the B-21.