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

A U.S. Air Force F-22 Raptor fighter jet is seen after a performance ahead of the International Air and Space Fair (FIDAE) at the Arturo Merino Benitez international airport in Santiago, Chile March 29, 2016. REUTERS/Rodrigo Garrido

A U.S. Air Force F-22 Raptor fighter jet pilot waves before taking off ahead of the International Air and Space Fair (FIDAE) at Santiago international airport, March 28, 2016. REUTERS/Ivan Alvarado 

A U.S. Air Force F-22 Raptor fighter jet performs ahead of the International Air and Space Fair (FIDAE) at Santiago international airport, March 28, 2016. REUTERS/Ivan Alvarado 

A U.S. Air Force F-22 Raptor fighter jet performs ahead of the International Air and Space Fair (FIDAE) at Santiago international airport, March 28, 2016. REUTERS/Ivan Alvarado 

A U.S. Air Force F-22 Raptor fighter jet prepares to take off ahead of the International Air and Space Fair (FIDAE) at Santiago international airport, March 28, 2016. REUTERS/Ivan Alvarado 

A U.S. Air Force F-22 Raptor fighter jet performs ahead of the International Air and Space Fair (FIDAE) at Santiago international airport, March 28, 2016. REUTERS/Ivan Alvarado 

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

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 U.S. Air Force F-22 Raptor fighter jet piloted by Major John Cummings performs maneuvers during the California International Airshow in Salinas, California, September 27, 2015. REUTERS/Michael Fiala 

A U.S. Air Force F-22 Raptor fighter jet piloted by Major John Cummings performs maneuvers during the California International Airshow in Salinas, California, September 27, 2015. REUTERS/Michael Fiala 

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 

A U.S. Air Force F-22 Raptor fighter jet piloted by Major John Cummings performs maneuvers during the California International Airshow in Salinas, California, September 27, 2015. REUTERS/Michael Fiala 

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 

A U.S. Air Force F-22 Raptor fighter jet piloted by Major John Cummings performs maneuvers during the California International Airshow in Salinas, California, September 27, 2015. REUTERS/Michael Fiala 

A boom operator of a KC-135 Stratotanker from the 100th Air Refueling Wing from the Royal Air Force Base Mildenhall, Britain refuels a F-22 Raptor fighter over the Baltic Sea on its way to 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 

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

Eric Kordus, a F-22 Raptor fighter jet pilot of the 95th Fighter Squadron from Tyndall, Florida, carries "Mr. Bone", the squadron's mascot consisting of a dressed-up plastic skeleton with a stovepipe hat and a moustache, after a refuelling mission of a KC-135 Stratotanker from the NATO airbase of Aemari, Estonia to Spangdahlem, 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 

Eric Kordus, a F-22 Raptor fighter jet pilot of the 95th Fighter Squadron from Tyndall, Florida, carries "Mr. Bone", the squadron's mascot consisting of a dressed-up plastic skeleton with a stovepipe hat and a moustache, after a refuelling mission of a KC-135 Stratotanker from the NATO airbase of Aemari, Estonia to Spangdahlem, 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 

Eric Kordus, a F-22 Raptor fighter jet pilot of the 95th Fighter Squadron from Tyndall, Florida, carries "Mr. Bone", the squadron's mascot consisting of a dressed-up plastic skeleton with a stovepipe hat and a moustache, after a refuelling mission of a KC-135 Stratotanker from the NATO airbase of Aemari, Estonia to Spangdahlem, 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 

Eric Kordus, a F-22 Raptor fighter jet pilot of the 95th Fighter Squadron from Tyndall, Florida, carries "Mr. Bone", the squadron's mascot consisting of a dressed-up plastic skeleton with a stovepipe hat and a moustache, after a refuelling mission of a KC-135 Stratotanker from the NATO airbase of Aemari, Estonia to Spangdahlem, 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 

"Mr. Bone", the mascot of the F-22 Raptor fighter jet pilots of the 95th Fighter Squadron from Tyndall, Florida, a dressed-up plastic skeleton with a stovepipe hat and a moustache, sits in the seats of a refuelling aircraft KC-135 Stratotanker during a refuelling mission from the NATO airbase of Aemari, Estonia to Spangdahlem, 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 

Estonia's Minister of Defence Sven Mikser stands in front of a F-22 Raptor fighter jet of the 95th Fighter Squadron from Tyndall at the newly established NATO airbase of Aemari near Tallinn, 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 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 

L-R Estonian air force commander Colonel Jaak Tarien, Estonian Minister of Defence Sven Mikser and U.S. air force Lieutnant Colonel Daniel Lehoski, commander of the 95th Fighter Squadron from Tyndall, Florida, pose in front of a F-22 Raptor fighter at the newly established NATO airbase of Aemari near Tallinn, 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 

Estonian Minister of Defence Sven Mikser and Lieutnant Colonel Daniel Lehoski, commander of the 95th Fighter Squadron from Tyndall, Florida, pose in front of a F-22 Raptor fighter at the newly established NATO airbase of Aemari near Tallinn, 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 

Boom operator Andrew Valence from Anderson, South Carolina operates the refueling nozzle of a KC-135 Stratotanker from the 100th Air Refueling Wing at the Royal Air Fore Base in Mildenhall in Britain to refuel a F-22 Raptor fighter over the Baltic Sea on its way to Aemeri air base, 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 

A weapon is placed in front of an U.S. Air Force F-22 Raptor fighter jet during a briefing in a hangar at the U.S. Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

Soldiers stand in front of an U.S. Air Force F-22 Raptor fighter jet during a briefing in a hangar at the U.S. Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

A soldier stands in front of an U.S. Air Force F-22 Raptor fighter jet during a briefing in a hangar at the U.S. Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

USAF Lieutenant colonel Daniel Lehoski stands in front of an U.S. Air Force F-22 Raptor fighter jet during a briefing in a hangar at the U.S. Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

Soldiers stand in front of an U.S. Air Force F-22 Raptor fighter jet during a briefing in a hangar at the U.S. Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

Soldiers listen in front of an U.S. Air Force F-22 Raptor fighter jet during a briefing in a hangar at the U.S. Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

A U.S. Air Force F-22 Raptor fighter jet taxis on tarmac at the Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

A U.S. Air Force F-22 Raptor fighter jet taxis on tarmac at the Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

Two U.S. Air Force F-22 Raptor fighter jets taxi on tarmac at the Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

A U.S. Air Force F-22 Raptor fighter jet flies over the Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

A U.S. Air Force F-22 Raptor fighter jet taxis on tarmac at the Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

A pilot sits in the cockpit of U.S. Air Force F-22 Raptor fighter jet at the Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

A U.S. Air Force F-22 Raptor fighter jet flies over the Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

A U.S. Air Force F-22 Raptor fighter jet flies at low altitude over the Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

A U.S. Air Force F-22 Raptor fighter jet flies at low altitude over the Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

A U.S. Air Force F-22 Raptor fighter jet flies at low altitude over the Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

A U.S. Air Force F-22 Raptor fighter jet flies at low altitude over the Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender 

A U.S. Air Force F-22 Raptor fighter jet flies at low altitude over the Spangdahlem Air base, Germany September 3, 2015. REUTERS/Ina Fassbender