U.S. pilot Dan Naim poses for a photograph in front of U.S. F-22 Raptor fighters parked on the runway at Mihail Kogalniceanu air base in Romania April 25, 2016. REUTERS/Toby Melville 

Two U.S. F-22 Raptor fighters fly over European airspace during a flight to Britain from Mihail Kogalniceanu air base in Romania April 25, 2016. REUTERS/Toby Melville 

A pilot looks up from a U.S. F-22 Raptor fighter as it prepares to refuel in mid-air with a KC-135 refuelling plane over European airspace during a flight to Britain from Mihail Kogalniceanu air base in Romania April 25, 2016. REUTERS/Toby Melville 

A pilot looks up from a U.S. F-22 Raptor fighter as it prepares to refuel in mid-air with a KC-135 refuelling plane over European airspace during a flight to Britain from Mihail Kogalniceanu air base in Romania April 25, 2016. REUTERS/Toby Melville 

A U.S. F-22 Raptor fighter flies over European airspace during a flight to Britain from Mihail Kogalniceanu air base in Romania April 25, 2016. REUTERS/Toby Melville 

A pilot looks up from a U.S. F-22 Raptor fighter at a fuel boom as it prepares to refuel in mid-air with a KC-135 plane over European airspace during a flight to Britain from Mihail Kogalniceanu air base in Romania April 25, 2016. REUTERS/Toby Melville 

A pilot looks up from a U.S. F-22 Raptor fighter as it prepares to refuel in mid-air with a KC-135 refuelling plane over European airspace during a flight to Britain from Mihail Kogalniceanu air base in Romania April 25, 2016. REUTERS/Toby Melville TPX IMAGES OF THE DAY

U.S. F-22 Raptor fighters fly alongside a KC-135 refueling plane over European airspace, during a flight from Britain to Mihail Kogalniceanu air base in Romania April 25, 2016. REUTERS/Toby Melville

U.S. F-22 Raptor fighters fly alongside a KC-135 refueling plane over European airspace, during a flight from Britain to Mihail Kogalniceanu air base in Romania April 25, 2016. REUTERS/Toby Melville

A U.S. F-22 Raptor fighter flies alongside a KC-135 refueling plane over European airspace, during a flight from Britain to Mihail Kogalniceanu air base in Romania April 25, 2016. REUTERS/Toby Melville

A U.S. F-22 Raptor fighter flies alongside a KC-135 refueling plane over European airspace, during a flight from Britain to Mihail Kogalniceanu air base in Romania April 25, 2016. REUTERS/Toby Melville

A U.S. F-22 Raptor fighter flies alongside a KC-135 refueling plane over European airspace, during a flight from Britain to Mihail Kogalniceanu air base in Romania April 25, 2016. REUTERS/Toby Melville

U.S. F-22 stealth fighter jets fly over Osan Air Base in Pyeongtaek, South Korea, February 17, 2016. REUTERS/Kim Hong-Ji TPX IMAGES OF THE DAY

A U.S. army soldier stands guard in front of a F-22 stealth fighter jet flies over Osan Air Base in Pyeongtaek, South Korea, February 17, 2016. REUTERS/Kim Hong-Ji 

A U.S. F-22 stealth fighter jet flies over Osan Air Base in Pyeongtaek, South Korea, February 17, 2016. REUTERS/Kim Hong-Ji 

Lieutenant general Terrence O'Shaughnessy (L), 7th Air Force commander of the U.S. Forces to Korea, and South Korean Air Forces Commander Lee Wang-geun shakes hands after a media briefing in front of a F-22 stealth fighter jet at Osan Air Base in Pyeongtaek, South Korea, February 17, 2016. REUTERS/Kim Hong-Ji 

A U.S. army soldier stands guard in front of a F-22 stealth fighter jet (R) and F-15 fighter jet at Osan Air Base in Pyeongtaek, South Korea, February 17, 2016. REUTERS/Kim Hong-Ji 

A U.S. F-22 stealth fighter jet lands at Osan Air Base in Pyeongtaek, South Korea, February 17, 2016. REUTERS/Kim Hong-Ji 

Members of Japan Air Self-Defense Force's (JASDF) stand in front of a prototype of the first Japan-made stealth fighter is pictured at a Mitsubishi Heavy Industries' factory in Toyoyama town, Aichi Prefecture, central Japan, January 28, 2016. Picture taken January 28, 2016. REUTERS/Kiyoshi Takenaka 

A prototype of the first Japan-made stealth fighter is pictured at a Mitsubishi Heavy Industries' factory in Toyoyama town, Aichi Prefecture, central Japan, January 28, 2016. Picture taken January 28, 2016. REUTERS/Kiyoshi Takenaka 

A prototype of the first Japan-made stealth fighter is pictured at a Mitsubishi Heavy Industries' factory in Toyoyama town, Aichi Prefecture, central Japan, January 28, 2016. Picture taken January 28, 2016. REUTERS/Kiyoshi Takenaka 

Pilot Kevin Eldridge in a P-51 Mustang and an F-22 Raptor fighter jet piloted by Major John Cummings perform a U.S. Air Force Heritage Flight at the California International Airshow in Salinas, California, September 27, 2015. A Heritage Flight involves a current USAF fighter aircraft flying in formation with a vintage fighter. REUTERS/Michael Fiala TPX IMAGES OF THE DAY

A visitor tries to look at the bottom of a model of J-31stealth fighter at Aviation Industry Corporation of China (AVIC)'s booth at the Aviation Expo China 2015, in Beijing, China, September 16, 2015. The four-day Aviation Expo China 2015 kicked off on Wednesday. According to local media, the expo is jointly organized by Aviation Industry Corporation of China (AVIC), Commercial Aircraft Corporation of China Ltd. (COMAC) and etc. Around 150 exhibitors from 16 countries were invited. REUTERS/Jason Lee 

A visitor rests next to a billboard showing the signs of Chinese Air Force's fighters and helicopters, which are made by Aviation Industry Corporation of China (AVIC), at the Aviation Expo China 2015, in Beijing, China, September 16, 2015. The four-day Aviation Expo China 2015 kicked off on Wednesday. According to local media, the expo is jointly organized by Aviation Industry Corporation of China (AVIC), Commercial Aircraft Corporation of China Ltd. (COMAC) and etc. Around 150 exhibitors from 16 countries were invited. REUTERS/Jason Lee 

Visitors look at a model of J-31 stealth fighter at Aviation Industry Corporation of China (AVIC)'s booth at the Aviation Expo China 2015, in Beijing, China, September 16, 2015. The four-day Aviation Expo China 2015 kicked off on Wednesday. According to local media, the expo is jointly organized by Aviation Industry Corporation of China (AVIC), Commercial Aircraft Corporation of China Ltd. (COMAC) and etc. Around 150 exhibitors from 16 countries were invited. REUTERS/Jason Lee 

Visitors look at a model of J-31 stealth fighter at Aviation Industry Corporation of China (AVIC)'s booth at the Aviation Expo China 2015, in Beijing, China, September 16, 2015. The four-day Aviation Expo China 2015 kicked off on Wednesday. According to local media, the expo is jointly organized by Aviation Industry Corporation of China (AVIC), Commercial Aircraft Corporation of China Ltd. (COMAC) and etc. Around 150 exhibitors from 16 countries were invited. REUTERS/Jason Lee 

A visitor takes a selfie in front of a model of J-31 stealth fighter at Aviation Industry Corporation of China (AVIC)'s booth at the Aviation Expo China 2015, in Beijing, China, September 16, 2015. The four-day Aviation Expo China 2015 kicked off on Wednesday. According to local media, the expo is jointly organized by Aviation Industry Corporation of China (AVIC), Commercial Aircraft Corporation of China Ltd. (COMAC) and etc. Around 150 exhibitors from 16 countries were invited. REUTERS/Jason Lee 

Foreign visitors stand next to a model of J-31 stealth fighter at Aviation Industry Corporation of China (AVIC)'s booth at the Aviation Expo China 2015, in Beijing, China, September 16, 2015. The four-day Aviation Expo China 2015 kicked off on Wednesday. According to local media, the expo is jointly organized by Aviation Industry Corporation of China (AVIC), Commercial Aircraft Corporation of China Ltd. (COMAC) and etc. Around 150 exhibitors from 16 countries were invited. REUTERS/Jason Lee 

Foreign visitors look at a model of J-31 stealth fighter at Aviation Industry Corporation of China (AVIC)'s booth at the Aviation Expo China 2015, in Beijing, China, September 16, 2015. The four-day Aviation Expo China 2015 kicked off on Wednesday. According to local media, the expo is jointly organized by Aviation Industry Corporation of China (AVIC), Commercial Aircraft Corporation of China Ltd. (COMAC) and etc. Around 150 exhibitors from 16 countries were invited. REUTERS/Jason Lee 

A F-22 Raptor fighter jet of the 95th Fighter Squadron from Tyndall, Florida is seen during refuelling by a KC-135 Stratotanker from the 100th Air Refueling Wing at the Royal Air Force Base in Mildenhall in Britain as they fly over the Baltic Sea towards Spangdahlem airbase, Germany September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay 

A F-22 Raptor fighter jet of the 95th Fighter Squadron from Tyndall, Florida approaches for refuelling by a KC-135 Stratotanker from the 100th Air Refueling Wing at the Royal Air Force Base in Mildenhall in Britain as they fly over the Baltic Sea towards Spangdahlem airbase, Germany September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay 

The heads-up display of a F-22 Raptor fighter jet reflects the sunlight as a pilot of the 95th Fighter Squadron from Tyndall, Florida is seen during refuelling by a KC-135 Stratotanker from the 100th Air Refueling Wing at the Royal Air Force Base in Mildenhall in Britain as they fly over the Baltic Sea towards Spangdahlem airbase, Germany September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay 

A F-22 Raptor fighter jet of the 95th Fighter Squadron from Tyndall, Florida is seen during refuelling by a KC-135 Stratotanker from the 100th Air Refueling Wing at the Royal Air Force Base in Mildenhall in Britain as they fly over the Baltic Sea towards Spangdahlem airbase, Germany September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay 

The head-up display of a F-22 Raptor fighter jet reflects the sun light as a pilot of the 95th Fighter Squadron from Tyndall, Florida is seen during refuelling by a KC-135 Stratotanker from the 100th Air Refueling Wing at the Royal Air Force Base in Mildenhall in Britain as they fly over the Baltic Sea towards Spangdahlem airbase, Germany September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay TPX IMAGES OF THE DAY

Two F-22 Raptor fighter jets of the 95th Fighter Squadron from Tyndall, Florida approach the KC-135 Stratotanker refuelling aircraft from the 100th Air Refueling Wing at the Royal Air Fore Base Mildenhall, Britain as they fly towards the newly established NATO airbase of Aemari, Estonia September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay 

A F-22 Raptor fighter jet of the 95th Fighter Squadron from Tyndall, Florida, leaves the refuelling nozzle after being filled up over the Baltic Sea by a KC-135 Stratotanker from the 100th Air Refueling Wing from the Royal Air Force Base in Mildenhall, Britain on its way towards the newly established NATO airbase of Aemari, Estonia September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay 

A F-22 Raptor fighter jet of the 95th Fighter Squadron from Tyndall, Florida, is being refuelled over the Baltic Sea by a KC-135 Stratotanker from the 100th Air Refueling Wing from the Royal Air Force Base in Mildenhall, Britain on its way towards the newly established NATO airbase of Aemari, Estonia September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay 

A F-22 Raptor fighter jet of the 95th Fighter Squadron from Tyndall, Florida, approaches a KC-135 Stratotanker from the 100th Air Refueling Wing at the Royal Air Force Base in Mildenhall in Britain as they fly over the Baltic Sea towards the newly established NATO airbase of Aemari, Estonia September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay 

Two F-22 Raptor fighter jets of the 95th Fighter Squadron from Tyndall, Florida, and an A-10 Thunderbolt (R) from Whiteman air force base, Missouri, approach the refuelling nozzle of a KC-135 Stratotanker from the 100th Air Refueling Wing at the Royal Air Fore Base in Mildenhall in Britain as they fly near the Estonian capital of Tallinn towards the newly established NATO airbase of Aemari, Estonia September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay 

Two F-22 Raptor fighter jets of the 95th Fighter Squadron from Tyndall, Florida and two A-10 Thunderbolt (R) from Whiteman air force base, Missouri approach the refuelling aircraft KC-135 Stratotanker from the 100th Air Refueling Wing at the Royal Air Fore Base in Mildenhall in Britain as they fly near the Estonian capital of Tallinn towards the newly established NATO airbase of Aemari, Estonia September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay TPX IMAGES OF THE DAY

A F-22 Raptor fighter jet of the 95th Fighter Squadron from Tyndall, Florida approaches a KC-135 Stratotanker from the 100th Air Refueling Wing at the Royal Air Force Base in Mildenhall in Britain as they fly over the Baltic Sea towards the newly established NATO airbase of Aemari, Estonia September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay 

A F-22 Raptor fighter jet of the 95th Fighter Squadron from Tyndall, Florida approaches a KC-135 Stratotanker from the 100th Air Refueling Wing at the Royal Air Force Base in Mildenhall in Britain as they fly over the Baltic Sea towards the newly established NATO airbase of Aemari, Estonia September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay 

Two F-22 Raptor fighter jets of the 95th Fighter Squadron from Tyndall, Florida approach the refuelling nozzle of a KC-135 Stratotanker from the 100th Air Refueling Wing at the Royal Air Fore Base in Mildenhall in Britain as they fly over the Baltic Sea towards the newly established NATO airbase of Aemari, Estonia September 4, 2015. Four F-22 Raptors and some 60 airmen were deployed to Spangdahlem Air Base, western Germany, to train with allied air forces such as Poland and Estonia. The first-ever training deployment of the 5th fighter generation to Europe is part of the European Reassurance Initiative. REUTERS/Wolfgang Rattay 

An F16 (L), F22 (C), and B25 Liberator fly over Battery Park in New York August 27, 2015. REUTERS/Lucas Jackson

Military aircraft fly over the Spire of One World Trade Center tower in lower Manhattan in New York August 27, 2015. REUTERS/Brendan McDermid 

Military aircraft fly over One World Trade Center tower and lower Manhattan in New York August 27, 2015. REUTERS/Brendan McDermid TPX IMAGES OF THE DAY

A B-2 Stealth Bomber performs a flyover at the 126th Rose Parade in Pasadena, California January 1, 2015. REUTERS/David McNew (UNITED STATES - Tags: TRANSPORT MILITARY ANNIVERSARY) 

A J-31 stealth fighter (background) of the Chinese People's Liberation Army Air Force lands on a runway after a flying performance at the 10th China International Aviation and Aerospace Exhibition in Zhuhai, Guangdong province, November 11, 2014. China unveiled a sophisticated new stealth fighter jet at an air show on Tuesday, a show of muscle during a visit by U.S. President Barack Obama for an Asia-Pacific summit. China hopes the much-anticipated J-31 stealth aircraft, developed by the Aviation Industry Corp of China (Avic), the country's top aircraft maker, will compete with U.S.-made hardware in export markets. REUTERS/Alex Lee (CHINA - Tags: TRANSPORT MILITARY) 

A J-31 stealth fighter of Chinese People's Liberation Army Air Force is seen during a test flight ahead of the 10th China International Aviation and Aerospace Exhibition in Zhuhai, Guangdong province, November 10, 2014. More than 130 planes will attend the six-day air show starting on Tuesday, Xinhua News Agency reported. REUTERS/Alex Lee (CHINA - Tags: MILITARY TRANSPORT) 

A J-31 stealth fighter of the Chinese People's Liberation Army Air Force is seen during a test flight ahead of the 10th China International Aviation and Aerospace Exhibition in Zhuhai, Guangdong province, November 10, 2014. More than 130 planes will attend the six-day air show starting on Tuesday, Xinhua News Agency reported. REUTERS/Alex Lee (CHINA - Tags: MILITARY TRANSPORT) 

Ron Hackworth flies a Northrop N9MB Flying Wing, designed in 1944 and considered the grandfather of the B-2 Stealth Bomber, over Navy Blue Angels F/A-18 Hornet fighter jets on the tarmac at the Los Angeles County Air Show at the General William J. Fox Airfield in Lancaster, California, March 21, 2014. REUTERS/David McNew (UNITED STATES - Tags: TRANSPORT MILITARY) 

Ron Hackworth taxis an experimental Northrop N9MB Flying Wing, designed in 1944 and considered the grandfather of the B-2 Stealth Bomber, past Blue Angeles F/A-18 Hornet fighter jets on rehearsal day for the Los Angeles County Air Show at the General William J. Fox Airfield in Lancaster, California, March 20, 2014. The air show will take place on Friday March 21 and Saturday March 22. REUTERS/David McNew (UNITED STATES - Tags: MILITARY TRANSPORT) 

F-22 stealth fighter jets belonging to the U.S. Air Force take off at a U.S. air force base in Osan, south of Seoul April 3, 2013. The U.S. has positioned a warship off the Korean coast as a shield against ballistic missile attack, and also deployed radar-evading F-22 Raptors on Sunday to take part in the annual joint military drills it carries out with South Korea. REUTERS/Lee Jae-Won (SOUTH KOREA - Tags: MILITARY POLITICS) 

F-22 stealth fighter jets belonging to the U.S. Air Force move to take off at a U.S. air force base in Osan, south of Seoul April 3, 2013. The U.S. has positioned a warship off the Korean coast as a shield against ballistic missile attack, and also deployed radar-evading F-22 Raptors on Sunday to take part in the annual joint military drills it carries out with South Korea. REUTERS/Lee Jae-Won (SOUTH KOREA - Tags: MILITARY POLITICS) 

A F-22 stealth fighter jet belonging to the U.S. Air Force takes off at a U.S. air force base in Osan, south of Seoul April 3, 2013. The U.S. has positioned a warship off the Korean coast as a shield against ballistic missile attack, and also deployed radar-evading F-22 Raptors on Sunday to take part in the annual joint military drills it carries out with South Korea. REUTERS/Lee Jae-Won (SOUTH KOREA - Tags: MILITARY POLITICS TRANSPORT) 

F-22 stealth fighter jets belonging to the U.S. Air Force move to take off at a U.S. air force base in Osan, south of Seoul April 3, 2013. The U.S. has positioned a warship off the Korean coast as a shield against ballistic missile attack, and also deployed radar-evading F-22 Raptors on Sunday to take part in the annual joint military drills it carries out with South Korea. REUTERS/Lee Jae-Won (SOUTH KOREA - Tags: MILITARY POLITICS) 

F-22 stealth fighter jets belonging to the U.S. Air Force move to take off at a U.S. air force base in Osan, south of Seoul April 3, 2013. The U.S. has positioned a warship off the Korean coast as a shield against ballistic missile attack, and also deployed radar-evading F-22 Raptors on Sunday to take part in the annual joint military drills it carries out with South Korea. REUTERS/Lee Jae-Won (SOUTH KOREA - Tags: MILITARY POLITICS) 

A military officer from Yemen poses with a Chinese attendant in front of a model of a plane with a scale of 1:4, believed to be the Shenyang J-31 stealth fighter, being displayed at the section for People's Liberation Army (PLA) Airforce, on the first day of the China International Aviation & Aerospace Exhibition in the southern Chinese city of Zhuhai November 13, 2012. REUTERS/Bobby Yip (CHINA - Tags: MILITARY TRANSPORT BUSINESS) 

A TV crew works in front of a scaled model of a plane, believed to be the Shenyang J-31 stealth fighter, on display at the section for People's Liberation Army Airforce, as part of the China International Aviation & Aerospace Exhibition in the southern Chinese city of Zhuhai November 12, 2012, one day before its official opening on Tuesday. REUTERS/Bobby Yip (CHINA - Tags: SCIENCE TECHNOLOGY TRANSPORT MILITARY MEDIA) 

A visitor looks at a scaled model of a plane, believed to be the Shenyang J-31 stealth fighter, on display at the section for People's Liberation Army Airforce, as part of the China International Aviation & Aerospace Exhibition in the southern Chinese city of Zhuhai November 12, 2012, one day before its official opening on Tuesday. REUTERS/Bobby Yip (CHINA - Tags: SCIENCE TECHNOLOGY TRANSPORT MILITARY)