A U.S. AV-8B Harrier aircraft lakes off on the flight deck of USS Boxer (LHD-4) in the Arabian Sea off Oman July 17, 2019. Picture taken July 17, 2019. REUTERS/Ahmed Jadallah 

U.S. Marines maintain an AV-8B Harrier aircraft on the flight deck of USS Boxer (LHD-4) in the Arabian Sea off Oman July 16, 2019. Picture taken July 16, 2019. REUTERS/Ahmed Jadallah 

A U.S. Navy officer watches as CH-53E Super Stallion aircraft attempts to land on the USS Boxer (LHD-4) in the Arabian Sea off Oman July 17, 2019. Picture taken July 17, 2019. REUTERS/Ahmed Jadallah 

A U.S CH-53E Super Stallion aircraft flies over a tanker in the Arabian Sea off Oman July 17, 2019. Picture taken July 17, 2019. REUTERS/Ahmed Jadallah 

Dutch Defence Minister Ank Bijleveld, Belgian counterpart Steven Vandeput, German counterpart Ursula von der Leyen, NATO Permanent Representative of Luxembourg Arlette Conzemius and Norway's Defence Minister Frank Bakke-Jensen attend a signing ceremony of the European multinational fleet of Airbus tanker transport aircraft during a NATO defence at the Alliance headquarters in Brussels, Belgium, February 14, 2018. REUTERS/Frederic Sierakowski/Pool 

Belgian Defence Minister Steven Vandeput and German counterpart Ursula von der Leyen attend a signing ceremony of the European multinational fleet of Airbus tanker transport aircraft during a NATO defence at the Alliance headquarters in Brussels, Belgium February 14, 2018. REUTERS/Frederic Sierakowski/Pool 

German Defence Minister Ursula von der Leyen attends a signing ceremony of the European multinational fleet of Airbus tanker transport aircraft during a NATO defence at the Alliance headquarters in Brussels, Belgium February 14, 2018. REUTERS/Frederic Sierakowski/Pool 

Dutch Defence Minister Ank Bijleveld, Belgian counterpart Steven Vandeput, German counterpart Ursula von der Leyen and Norway's counterpart Frank Bakke-Jensen attend a signing ceremony of the European multinational fleet of Airbus tanker transport aircraft during a NATO defence at the Alliance headquarters in Brussels, Belgium February 14, 2018. REUTERS/Frederic Sierakowski/Pool 

Total Chief Executive Patrick Pouyanne attends a ceremony of naming of a new Russian Arctic LNG tanker after Christophe de Margerie, the late CEO of French oil corporation Total S.A., who has died in an aircraft crash in Moscow on October 20, 2014, on the side line of the St. Petersburg International Economic Forum (SPIEF), Russia, June 3, 2017. REUTERS/Olga Maltseva/Pool 

Russian President Vladimir Putin walks to attend a ceremony of naming of a new Russian Arctic LNG tanker after Christophe de Margerie, the late CEO of French oil corporation Total S.A., who has died in an aircraft crash in Moscow on October 20, 2014, on the side line of the St. Petersburg International Economic Forum (SPIEF), Russia, June 3, 2017. REUTERS/Olga Maltseva/Pool 

Russian President Vladimir Putin attends a ceremony of naming of a new Russian Arctic LNG tanker after Christophe de Margerie, the late CEO of French oil corporation Total S.A., who has died in an aircraft crash in Moscow on October 20, 2014, on the side line of the St. Petersburg International Economic Forum (SPIEF), Russia, June 3, 2017. REUTERS/Olga Maltseva/Pool 

Russian President Vladimir Putin attends a ceremony of naming of a new Russian Arctic LNG tanker after Christophe de Margerie, the late CEO of French oil corporation Total S.A., who has died in an aircraft crash in Moscow on October 20, 2014, on the side line of the St. Petersburg International Economic Forum (SPIEF), Russia, June 3, 2017. REUTERS/Olga Maltseva/Pool 

Russian President Vladimir Putin attends a ceremony of naming of a new Russian Arctic LNG tanker after Christophe de Margerie, the late CEO of French oil corporation Total S.A., who has died in an aircraft crash in Moscow on October 20, 2014, on the side line of the St. Petersburg International Economic Forum (SPIEF), Russia, June 3, 2017. REUTERS/Olga Maltseva/Pool 

Ground crew refuel a wide body aircraft emblazoned with Amazon's Prime logo at Lehigh Valley International Airport in Allentown, Pennsylvania, U.S. December 20, 2016. Picture taken December 20, 2016. To match Insight AMAZON.COM-SHIPPING/ REUTERS/Mark Makela 

A British Royal Air Force Typhoon aircraft refuel from a tanker aircraft during a mission over central Iraq September 21, 2016. REUTERS/Petros Karadjias/Pool 

A British Royal Air Force Typhoon aircraft prepare for refuel from a tanker aircraft during a mission over central Iraq September 21, 2016. REUTERS/Petros Karadjias/Pool 

A British Royal Air Force Typhoon aircraft refuel from a tanker aircraft during a mission over central Iraq September 21, 2016. REUTERS/Petros Karadjias/Pool 

A British Royal Air Force Typhoon aircraft refuel from a tanker aircraft during a mission over central Iraq September 21, 2016. REUTERS/Petros Karadjias/Pool 

A British Royal Air Force Typhoon aircraft refuel from a tanker aircraft during a mission over central Iraq September 21, 2016. REUTERS/Petros Karadjias/Pool 

A British Royal Air Force Typhoon aircraft refuel from a tanker aircraft during a mission over central Iraq September 21, 2016. REUTERS/Petros Karadjias/Pool 

A British Royal Air Force Typhoon aircraft refuel from a tanker aircraft during a mission over central Iraq September 21, 2016. REUTERS/Petros Karadjias/Pool 

A British Royal Air Force Typhoon aircraft refuel from a tanker aircraft during a mission over central Iraq September 21, 2016. REUTERS/Petros Karadjias/Pool 

A British Royal Air Force Typhoon aircraft refuel from a tanker aircraft during a mission over central Iraq September 21, 2016. REUTERS/Petros Karadjias/Pool 

A British Royal Air Force Typhoon aircraft prepare for refuel from a tanker aircraft during a mission over central Iraq September 21, 2016. REUTERS/Petros Karadjias/Pool TPX IMAGES OF THE DAY 

The 10 Tanker Air Carrier DC-10 firefighting aircraft makes a drop to fight the Pilot Fire near Silverwood Lake in San Bernardino county near Hesperia, California August 7, 2016. REUTERS/Patrick T. Fallon 

The 10 Tanker Air Carrier DC-10 firefighting aircraft makes a drop to fight the Pilot Fire near Silverwood Lake in San Bernardino county near Hesperia, California August 7, 2016. REUTERS/Patrick T. Fallon 

A United States Air Force F-35A receives fuel from a KC-10 refueling tanker while flying over the Atlantic Ocean, June 30, 2016. REUTERS/Lucas Jackson TPX IMAGES OF THE DAY 

A C-130 air tanker makes a drop of fire retardant as a sky crane passes below over one of two wildfires in the Angeles National Forest above Azusa, California, U.S. June 20, 2016. REUTERS/Gene Blevins 

Canadian F-18 war planes (L) wait to refuel from a British VC-10 tanker aircraft over the Mediterranean Sea off Libya July 10, 2011. REUTERS/David Brunnstrom/File Photo

A crew member looks out of a KC-135 refuelling plane as a U.S. F-22 Raptor fighter prepares to connect to a fuel line 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 

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

A German air force Tornado jet takes off from the German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first of the German air force Tornado reconnaissance jets took off for Turkey's Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer 

A German air force Tornado jet takes off from the German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first of the German air force Tornado reconnaissance jets took off for Turkey's Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer 

A German air force Tornado jet takes off from the German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first of the German air force Tornado reconnaissance jets took off for Turkey's Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer 

A German air force Tornado jet takes off from the German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first of the German air force Tornado reconnaissance jets took off for Turkey's Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer TPX IMAGES OF THE DAY 

A German air force Tornado jet takes off from the German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first of the German air force Tornado reconnaissance jets took off for Turkey's Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer 

A German air force Tornado jet takes off from the German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first of the German air force Tornado reconnaissance jets took off for Turkey's Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer TPX IMAGES OF THE DAY 

A German airforce Airbus A400M military aircraft takes off from the German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first the German air force Tornado reconnaissance jets will take off for Turkey's Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer

A German airforce Airbus A400M military aircraft taxis along the runway at German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first the German air force Tornado reconnaissance jets will take off for Turkey's Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer

A German airforce Airbus A400M military aircraft taxis along the runway at German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first the German air force Tornado reconnaissance jets will take off for Turkey's Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer

Army personnel board a German airforce Airbus A400M military aircraft at German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first the German air force Tornado reconnaissance jets will take off for Turkey's Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer

Army personnel board a German airforce Airbus A400M military aircraft at German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first the German air force Tornado reconnaissance jets will take off for Turkey's Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer

A German airforce Airbus A400M military refuelling aircraft taxis along the runway at German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first the German air force Tornado reconnaissance jets will take off for Turkey?s Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer ( - Tags: TRANSPORT MILITARY) 

A German airforce Airbus A400M military refuelling aircraft taxis along the runway at German army Bundeswehr airbase in Jagel, northern Germany December 10, 2015. The first the German air force Tornado reconnaissance jets will take off for Turkey?s Incirlik air base on Thursday, to support the military campaign against Islamic State. REUTERS/Fabian Bimmer ( - Tags: TRANSPORT MILITARY) 

A drone operated by paramilitary police flies over the site of last week's explosions at Binhai new district in Tianjin, China, August 17, 2015. Many operations have resumed at China's Tianjin port, trade sources said, after explosions last week that killed more than 100 people and disrupted business at what is an important oil, gas and bulk import harbor for Asia's biggest economy. The explosions on Aug. 12 led to the disruption of all chemical and oil tanker discharges at the port, and imports of iron ore were also affected. REUTERS/Kim Kyung-Hoon TPX IMAGES OF THE DAY

Palestinians look at the remains of a missile which witnesses said was fired by an Israeli aircraft on a street in Deir El-Balah in the central Gaza Strip July 11, 2014. Israeli air strikes on Gaza killed four more Palestinians before dawn on Friday, raising the death toll from the four day offensive to at least 85, while a Palestinian rocket hit a fuel tanker at an Israeli petrol station causing a huge blaze. REUTERS/Ashraf Amrah (GAZA - Tags: POLITICS CIVIL UNREST) 

A DC-10 Super Tanker aircraft flies by after dumping flame retardant as firefighters battle a blaze in San Marcos, California May 14, 2014. California fire crews, helped by diminished overnight winds, made substantial headway by early Wednesday against a blaze that had prompted thousands of evacuations in and around San Diego for several hours while flames were at their peak. REUTERS/Sam Hodgson (UNITED STATES - Tags: ENVIRONMENT DISASTER) 

A DC-10 Super Tanker aircraft dumps flame retardant as firefighters battle a blaze in San Marcos, California May 14, 2014. California fire crews, helped by diminished overnight winds, made substantial headway by early Wednesday against a blaze that had prompted thousands of evacuations in and around San Diego for several hours while flames were at their peak. REUTERS/Sam Hodgson (UNITED STATES - Tags: ENVIRONMENT DISASTER) 

A "super scooper" air tanker makes waters drops as firefighters battle a fast-moving California wildfire, so-called the "Colby Fire", in the hills of Glendora January 16, 2014. The wildfire, started accidentally by three campers, roared out of control in foothills above Los Angeles on Thursday, destroying at least two homes and forcing more than 1,000 residents to flee, fire and law enforcement officials said. The wind-whipped blaze erupted before dawn in the Angeles National Forest north of Glendora, about 40 miles east of downtown Los Angeles in the foothills of the San Gabriel Mountains. REUTERS/Gene Blevins (UNITED STATES - Tags: DISASTER ENVIRONMENT TRANSPORT)