̣In what is being seen as a show of force, the U.S. flew two B-1B Lancer bombers over the North Korean demilitarized zone, the U.S Air Force said in a statement.

The drill happened Thursday as part of a 10-hour joint mission with South Korean and Japanese fighter jets, according to a statement by the Pacific Air Forces. The bombers flew from the Pacific island territory of Guam to the divided Korean peninsula where they were joined by the South Korean and the U.S. fighter jets. On their way back to Guam, the bombers flew with the Japanese fighter jets over the East China Sea, it added. The exercise came as tensions spiked after North Korea launched an ICBM Tuesday, raising the stakes in the international standoff over its nuclear weapons program.

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This the second time in four days that the B1 bomber has been used by the air force, with two of them flying over the disputed South China Sea on Wednesday in a bid to assert ‘freedom of navigation’ in the territory, despite China’s claims to all of the waterway.

The strategic bomber has been frequently used over the years and especially now against North Korea, after the latter’s regular testing of nuclear weapons.

Nicknamed ‘the Bone’, the B-1 is considered to be the backbone of the U.S.’ long-range bomber force. It can rapidly deliver massive quantities of precision (intended to hit a specific target) and non-precision weapons against any adversary. It is one of three strategic bombers (a long range penetration bomber designed to drop large amounts of air-to-ground weaponry onto a distant target) in the U.S. Air Force fleet as of 2017, the other two being the B-2 Spirit "Stealth Bomber" and the B-52 Stratofortress.

According to the website the National Interest, the highly versatile, multi-mission weapon system is manufactured by North American Rockwell/ Rockwell International, which is now a part of Boeing. The B-1A was initially developed in the 1970s as a replacement for the B-52, a jet-powered strategic bomber.

The U.S. Air Force stated that four prototypes of this long-range, high-speed strategic bomber were developed and tested in the mid-1970s. However, former President Jimmy Carter canceled the Lancer program on in 1977 during the Cold War, in favor of air-launched cruise missiles (carried onboard the B-52), intercontinental ballistic missiles and stealth bombers after it became apparent that penetrating Soviet airspace at high altitudes in a conventional non-stealthy aircraft, posed a danger.

Former President Ronald Reagan eventually revived the Lancer program in 1981, bringing out the B-1B, an improved variant. The new B-1B was optimized for low-level penetration among other upgrades. The resultant B-1B aircraft had much better survivability.

Following the Cold War, the Air Force removed the B-1B fleet’s nuclear capability and converted the aircraft into a conventional weapons platform. It performed very well in the conventional role in Iraq and Afghanistan.

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However, the Lancer cannot survive inside heavily defended airspace. At best, the B-1B can operate in a medium threat environment. The Air Force’s fleet of 20 B-2 stealth bombers is currently the service’s only strategic bombers that can penetrate deep into an area defended by advanced Russian or Chinese-made surface-to-air missile systems.

The B-1B holds almost 50 world records for speed, payload, range, and time of climb in its class. The National Aeronautic Association recognized the B-1B for completing one of the 10 most memorable record flights for 1994. Over the years, the Air Force has added a host of precision-guided munitions, data-links and sensors into the bomber to keep it relevant in the future.