Supporters of U.S. President Donald Trump wave flags as a U.S. Air Force B-52 bomber flies during Independence Day celebrations in Washington, U.S., July 4, 2020. REUTERS/Joshua Roberts

Wushu - 2018 Asian Games - Women's Sanda -52kg - JIExpo Kemayoran Hall B - Jakarta, Indonesia - August 23, 2018. Gold medallist Li Yueyao of China. REUTERS/Cathal Mcnaughton

Wushu - 2018 Asian Games - Women's Sanda -52kg - JIExpo Kemayoran Hall B - Jakarta, Indonesia - August 23, 2018. Gold medallist Li Yueyao of China, silver medallist Mansoryan Samiroumi Elaheh of Iran , bronze medallist Chen Weiting of Taiwan, Divine Wally of Philippines. REUTERS/Cathal Mcnaughton

Wushu - 2018 Asian Games - Women's Sanda -52kg final - JIExpo Kemayoran Hall B - Jakarta, Indonesia - August 23, 2018. Mansoryan Samiroumi Elaheh of Iran and Li Yueyao of China in action. REUTERS/Cathal Mcnaughton

Wushu - 2018 Asian Games - Women's Sanda -52kg final - JIExpo Kemayoran Hall B - Jakarta, Indonesia - August 23, 2018. Mansoryan Samiroumi Elaheh of Iran and Li Yueyao of China in action. REUTERS/Cathal Mcnaughton

Wushu - 2018 Asian Games - Women's Sanda -52kg final - JIExpo Kemayoran Hall B - Jakarta, Indonesia - August 23, 2018. Mansoryan Samiroumi Elaheh of Iran and Li Yueyao of China in action. REUTERS/Cathal Mcnaughton

U.S. bomber B-52 flies over during the final day of NATO Saber Strike exercises in Orzysz, Poland, June 16, 2017. REUTERS/Ints Kalnins

U.S. Air Force B-52 bomber flies during the annual recurring multinational, maritime-focused NATO exercise BALTOPS 2017 near Ventspils, Latvia June 6, 2017. REUTERS/Ints Kalnins

A U.S. B-52 bomber takes part in the "Saber Strike" NATO military exercise in Adazi, Latvia, June 13, 2016. REUTERS/Ints Kalnins

U.S. B52 planes flies during Exercise Eager Lion at one of the Jordanian military bases in Zarqa, east of Amman, Jordan, May 24, 2016. REUTERS/Muhammad Hamed

A U.S. B52 plane (R) flies during Exercise Eager Lion at one of the Jordanian military bases in Zarqa, east of Amman, Jordan, May 24, 2016. REUTERS/Muhammad Hamed

U.S. B52 planes flies during Exercise Eager Lion at one of the Jordanian military bases in Zarqa, east of Amman, Jordan, May 24, 2016. REUTERS/Muhammad Hamed

FILE PHOTO: A Boeing B-52 Stratofortress strategic bomber from the US Air Force Andersen Air Force Base in Guam performs a fly-over at the Singapore Airshow in Singapore February 14, 2012. REUTERS/Tim Chong/File Photo

A U.S. Air Force B-52 (C) flies over Osan Air Base in Pyeongtaek, South Korea, January 10, 2016. REUTERS/Kim Hong-Ji

A U.S. Air Force B-52 flies over Osan Air Base in Pyeongtaek, South Korea, January 10, 2016. REUTERS/Kim Hong-Ji

A U.S. Air Force B-52 flies over Osan Air Base in Pyeongtaek, South Korea, January 10, 2016. REUTERS/Kim Hong-Ji

A U.S. Air Force B-52 (R) flies over Osan Air Base in Pyeongtaek, South Korea, January 10, 2016. REUTERS/Kim Hong-Ji TPX IMAGES OF THE DAY

A U.S. B52 plane is pictured during Exercise Eager Lion at the Jordan-Saudi Arabia border, south of Amman May 18, 2015. Around 10,000 participants from 18 countries will take part in Eager Lion. REUTERS/Muhammad Hamed

A U.S. B52 plane is pictured during Exercise Eager Lion at the Jordan-Saudi Arabia border, south of Amman May 18, 2015. Around 10,000 participants from 18 countries will take part in Eager Lion. REUTERS/Muhammad Hamed

Captain Fleming Thompson works on the navigation desk of his U.S. Air Force B-52 during a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS)

Captains Fleming Thompson (L) and Rylan Kabanuck work on the navigation desk of a U.S. Air Force B-52 during a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS)

Part of the instrument panel on a U.S Air Force B-52 is seen during a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS)

Captain Creighton Moorman flies his U.S. Air Force B-52 as another prepares for a mid-air refuel during a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS)

A U.S. Air Force B-52 is seen through the window of another as it prepares for a mid-air refuel during a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS)

A U.S Air Force B-52 is seen through the window of another during a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS)

Major Steve Miracle flies his U.S. Air Force B-52 during a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS)

A U.S. Air Force B-52 is seen through the window of another during a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS)

Major Steve Miracle flies his U.S Air Force B-52 as another flies alongside during a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: MILITARY POLITICS)

A U.S. Air Force B-52 is seen through the window of another during a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS)

Captain Andrew Paulsen walks in front of his U.S. Air Force B-52 during pre-flight checks at Royal Air Force (RAF) Fairford before a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS)

The throttle levers of a U.S. Air Force B-52 are seen before take off at Royal Air Force (RAF) Fairford ahead of a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS)

A U.S. Air Force B-52 goes through its pre-flight checks at Royal Air Force (RAF) Fairford before a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS)

A member of the ground crew prepares the bomb doors of a U.S. Air Force B-52 during pre-flight checks at Royal Air Force (RAF) Fairford before a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: MILITARY POLITICS TRANSPORT)

Captain Andrew Paulsen looks into the bomb bay of his U.S. Air Force B-52 during pre-flight checks at Royal Air Force (RAF) Fairford before a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: MILITARY POLITICS TRANSPORT)

Major Steve Miracle walks under the bomb doors of his U.S. Air Force B-52 during pre-flight checks at Royal Air Force (RAF) Fairford before a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: MILITARY POLITICS TRANSPORT)

A U.S. Air Force B-52 goes through its pre-flight checks at Royal Air Force (RAF) Fairford before a training mission in the United Kingdom's airspace, June 17, 2014. Several B-52s are on a training deployment at Fairford, in central England. REUTERS/Andrew Winning (BRITAIN - Tags: TRANSPORT MILITARY POLITICS TPX IMAGES OF THE DAY)

Germany's Felix Schutz (L) battles for the puck with Kazakhstan's Anton Kazantsev (52) as goalie Vitali Yeremeyev (R) defends during the second period of their men's ice hockey World Championship Group B game at Minsk Arena in Minsk May 10, 2014. Reuters/Alexander Demianchuk (BELARUS - Tags: SPORT ICE HOCKEY)

Kazakhstan's Andrei Gavrilin (33) and Anton Kazantsev (52) battle for the puck with Germany's Daniel Pietta (R) during the first period of their men's ice hockey World Championship Group B game at Minsk Arena in Minsk May 10, 2014. Reuters/Alexander Demianchuk (BELARUS - Tags: SPORT ICE HOCKEY)

Kate Pierson, from The B-52's, poses as she arrives at the 55th annual Grammy Awards in Los Angeles, California February 10, 2013. REUTERS/Mario Anzuoni (UNITED STATES - Tags: ENTERTAINMENT) (GRAMMYS-ARRIVALS)

Artistes perform during celebrations to mark the 40th anniversary of the Linebacker 2 bombing campaign at the National Convention Center in Hanoi December 29, 2012. Vietnam marks the 40th anniversary of the Linebacker 2 campaign, also known as the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousands of residents were killed and 81 U.S. aircraft shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: POLITICS MILITARY ANNIVERSARY SOCIETY)

Artistes perform during celebrations to mark the 40th anniversary of the Linebacker 2 bombing campaign at the National Convention Center in Hanoi December 29, 2012. Vietnam marks the 40th anniversary of the Linebacker 2 campaign, also known as the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousands of residents were killed and 81 U.S. aircraft shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: POLITICS MILITARY ANNIVERSARY SOCIETY)

Artistes perform during celebrations to mark the 40th anniversary of the Linebacker 2 bombing campaign at the National Convention Center in Hanoi December 29, 2012. Vietnam marks the 40th anniversary of the Linebacker 2 campaign, also known as the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousands of residents were killed and 81 U.S. aircraft shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: POLITICS MILITARY ANNIVERSARY SOCIETY)

A veteran with medals pinned onto his ceremonial uniform attends celebrations to mark the 40th anniversary of the Linebacker 2 bombing campaign at the National Convention Center in Hanoi December 29, 2012. Vietnam marks the 40th anniversary of the Linebacker 2 campaign, also known as the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousands of residents were killed and 81 U.S. aircraft shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: POLITICS MILITARY ANNIVERSARY SOCIETY)

Performers sing in front of a poster promoting celebrations to mark the 40th anniversary of the Linebacker 2 bombing campaign at the National Convention Center in Hanoi December 29, 2012. Vietnam marks the 40th anniversary of the Linebacker 2 campaign, also known as the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousands of residents were killed and 81 U.S. aircraft shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: MILITARY ANNIVERSARY CONFLICT SOCIETY)

Vietnamese military cadets line up in front of a giant poster promoting the celebrations to mark the 40th anniversary of the Linebacker 2 bombing campaign at the National Convention Center in Hanoi December 29, 2012. Vietnam marks the 40th anniversary of the Linebacker 2 campaign, also known as the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousands of residents were killed and 81 U.S. aircraft shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: POLITICS MILITARY ANNIVERSARY SOCIETY)

Veterans attend celebrations to mark the 40th anniversary of the Linebacker 2 bombing campaign at the National Convention Center in Hanoi December 29, 2012. Vietnam marks the 40th anniversary of the Linebacker 2 campaign, also known as the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousands of residents were killed and 81 U.S. aircraft shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: POLITICS MILITARY ANNIVERSARY SOCIETY)

Veterans attend celebrations to mark the 40th anniversary of the Linebacker 2 bombing campaign at the National Convention Center in Hanoi December 29, 2012. Vietnam marks the 40th anniversary of the Linebacker 2 campaign, also known as the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousands of residents were killed and 81 U.S. aircraft shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: POLITICS MILITARY ANNIVERSARY SOCIETY)

Vietnam's President Truong Tan Sang (L) waves as he stands next to Air Force Commander Lieutenant General Phuong Minh Hoa (2nd R) and Deputy Head of the Military General Department of Politics Lieutenant General Mai Quang Phan (R) after attending celebrations to mark the 40th anniversary of the Linebacker 2 bombing campaign at the National Convention Center in Hanoi December 29, 2012. Vietnam marks the 40th anniversary of the Linebacker 2 campaign, also known as the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousands of residents were killed and 81 U.S. aircraft shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: POLITICS MILITARY ANNIVERSARY SOCIETY)

Vietnam's President Truong Tan Sang (C, first row) is followed by military officers as he leaves celebrations to mark the 40th anniversary of the Linebacker 2 bombing campaign at the National Convention Center in Hanoi December 29, 2012. Vietnam marks the 40th anniversary of the Linebacker 2 campaign, also known as the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousands of residents were killed and 81 U.S. aircraft shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: MILITARY ANNIVERSARY CONFLICT SOCIETY)

A woman walks near a giant display with an image of a destroyed U.S. aircraft B52 commemorating the 40th anniversary of the Linebacker 2 bombing campaign on a street in Hanoi December 18, 2012. Vietnam marks the 40th anniversary of the Linebacker 2 campaign, also known as the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousands of residents were killed and 81 U.S. aircraft shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: MILITARY ANNIVERSARY CONFLICT SOCIETY TRANSPORT)

A visitor looks at combs, which were made from the wreckage of a U.S. B52 aircraft that was destroyed during the Linebacker II bombing campaign in December 1972, at an exhibition in Hanoi December 4, 2012. The exhibition displayed household items made from war relics collected by local Vietnamese journalist and veteran Nguyen Ngoc Tien. It was held as part of celebrations leading to the 40th anniversary of the "Christmas Bombing", the last airstrike operated by U.S. military between December 18 and December 30, 1972, during which Vietnam said thousand residents were killed while 81 U.S. aircraft were shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: ANNIVERSARY MILITARY SOCIETY)

Vietnamese journalist and veteran Nguyen Ngoc Tien poses for a photo next to an alarm gong, which was made from a bomb released by U.S. aircraft B52 during the Linebacker II bombing campaign in December 1972, at an exhibition in Hanoi December 4, 2012. The exhibition displayed household items made from war relics collected by Nguyen. It was held as part of celebrations leading to the 40th anniversary of the "Christmas Bombing", the last airstrike operated by U.S. military between December 18 and December 30, 1972, during which Vietnam said thousand residents were killed while 81 U.S. aircraft were shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAMA - Tags: SOCIETY ANNIVERSARY MILITARY MEDIA)

A man walks near a table and chairs, which were made from the wreckage of a U.S. aircraft B52 that was destroyed during the Linebacker II bombing campaign in December 1972, at an exhibition in Hanoi December 4, 2012. The exhibition displayed household items made from war relics collected by local Vietnamese journalist and veteran Nguyen Ngoc Tien. It was held as part of celebrations leading to the 40th anniversary of the "Christmas Bombing", the last airstrike operated by U.S. military between December 18 and December 30, 1972, during which Vietnam said thousand residents were killed while 81 U.S. aircraft were shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: SOCIETY ANNIVERSARY MILITARY)

A visitor looks at a flask, which was made from the wreckage of a U.S. aircraft B52 that was destroyed during the Linebacker II bombing campaign in December 1972, at an exhibition in Hanoi December 4, 2012. The exhibition displayed household items made from war relics collected by local Vietnamese journalist and veteran Nguyen Ngoc Tien. It was held as part of celebrations leading to the 40th anniversary of the "Christmas Bombing", the last airstrike operated by U.S. military between December 18 and December 30, 1972, during which Vietnam said thousand residents were killed while 81 U.S. aircraft were shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: SOCIETY ANNIVERSARY MILITARY)

A man touches part of a Russian missile SAM (C) which reads, "Determined to defeat American invaders", near a piece of wreckage (top L) from a U.S. aircraft B52 that was destroyed during the Linebacker II bombing campaign in December 1972, at an exhibition in Hanoi December 4, 2012. The exhibition displayed household items made from war relics collected by local Vietnamese journalist and veteran Nguyen Ngoc Tien. It was held as part of celebrations leading to the 40th anniversary of the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousand residents were killed while 81 U.S. aircraft were shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: SOCIETY ANNIVERSARY MILITARY)

A Vietnamese veteran looks at the rim, mudguard and chainguard of a bicycle, which were made from the wreckage of a U.S. aircraft B52 that was destroyed during the Linebacker II bombing campaign in December 1972, at an exhibition in Hanoi December 4, 2012. The exhibition displayed household items made from war relics collected by local Vietnamese journalist and veteran Nguyen Ngoc Tien. It was held as part of celebrations leading to the 40th anniversary of the "Christmas Bombing", the last airstrike operated by the U.S. military between December 18 and December 30, 1972, during which Vietnam said thousand residents were killed while 81 U.S. aircraft were shot down, 34 of them B52 planes. REUTERS/Kham (VIETNAM - Tags: ANNIVERSARY MILITARY SOCIETY)

A visitor walks past "Yellow" during the media preview of The Art of the Brick exhibition in Singapore November 15, 2012. The exhibition which features U.S. artist Nathan Sawaya's 52 original Lego creations starts from November 17, 2012 to April 14, 2013 at the Art Science Museum. REUTERS/Edgar Su (SINGAPORE - Tags: ENTERTAINMENT SOCIETY) FOR BEST QUALITY IMAGE: ALSO SEE GF2E94B00K201.