The B-52 Stratofortress aircraft, which arrived in Qatar, were based in Saudi Arabia and last flown operationally in May 2006 as part of the war in Afghanistan, air force officials said.
"The B-52 will provide the coalition continued precision and deliver desired air power effects," said Lieutenant General Charles Brown, commander of US Air Forces Central Command.
The long-range planes will provide "flexibility and endurance" in the US-led coalition campaign against the jihadists, he added.
"The B-52 demonstrates our continued resolve to apply persistent pressure on (the IS group) and defend the region in any future contingency," Brown said.
The B-52, the first US long-range heavy bomber, was developed to carry nuclear weapons and has been adapted over the years.
It has been used in missions in the Vietnam War, the 1991 Gulf War and in Afghanistan.
It was not immediately clear how many of the bombers had been deployed.
The Boeing B-52 Stratofortress is a long-range, subsonic, jet-powered strategic bomber.
The B-52 was designed and built by Boeing, which has continued to provide support and upgrades.
It has been operated by the United States Air Force (USAF) since the 1950s.
The bomber is capable of carrying up to 70,000 pounds (32,000 kg) of weapons, and has a typical combat range of more than 8,800 miles (14,080 km) with aerial refueling.
Built to carry nuclear weapons for Cold War-era deterrence missions, the B-52 Stratofortress replaced the Convair B-36.
A veteran of several wars, the B-52 has dropped only conventional munitions in combat.
The B-52 has been in active service with the USAF since 1955.
As of 2012, 85 were in active service with nine in reserve.
The bombers flew under the Strategic Air Command (SAC) until it was inactivated in 1992 and its aircraft absorbed into the Air Combat Command (ACC).
In 2010, all B-52 Superior performance at high subsonic speeds and relatively low operating costs have kept the B-52 in service despite the advent of later, more advanced aircraft, including the canceled Mach 3 B-70 Valkyrie, the variable-geometry B-1 Lancer, and the stealth B-2 Spirit.