Indonesian airforce personnel tidy up their CN235-220 maritime surveillance aircraft displayed at the Singapore Airshow at Changi Exhibition Center February 17, 2016. Picture taken February 17, 2016. REUTERS/Edgar Su

Indonesian airforce personnel stand next to their CN235-220 maritime surveillance aircraft displayed at the Singapore Airshow at Changi Exhibition Center February 17, 2016. Picture taken February 17, 2016. REUTERS/Edgar Su

Britain's Prime Minister David Cameron (6th L) speaks with military personnel as he stands between an RAF Sentinel surveillance aircraft (L) and an RAF Eurofighter Typhoon fighter jet during his visit to Royal Air Force station RAF Northolt in London, Britain November 23, 2015. Britain will invest an extra 12 billion pounds ($18 billion) in defense equipment over the next 10 years including nine Boeing submarine-hunting aircraft, Cameron said on Monday. REUTERS/Justin Tallis/pool

A tour group gathers under a Lockheed SR-71 Blackbird at the Udvar-Hazy Smithsonian National Air and Space Annex Museum in Chantilly, Virginia August 28, 2015. The SR-71 was a long-range spy plane that was in use from 1964 to 1998 and designed to operate at three times the speed of sound. REUTERS/Gary Cameron

A NATO AWACS (Airborne Warning and Control Systems) aircraft is seen on the tarmac as it prepares to take-off for a training mission from the AWACS air base in Geilenkirchen near the German-Dutch border April 16, 2014. NATO said on Wednesday it would send more ships, planes and troops to eastern Europe to reassure allies worried by Russia's annexation of Crimea but shied away from new permanent bases in the east as Poland wanted. REUTERS/Francois Lenoir (GERMANY - Tags: POLITICS MILITARY TRANSPORT TPX IMAGES OF THE DAY)

A U.S. military surveillance drone camera flies in Musa Qal-Ah district in Helmand province, southwestern Afghanistan November 2, 2012. REUTERS/Erik De Castro (AFGHANISTAN - Tags: MILITARY CIVIL UNREST)

An observation blimp flies over Forward Operating Base (FOB) Goode near the town of Gardez in Afghanistan's Paktia Province July 9, 2012. REUTERS/Lucas Jackson (AFGHANISTAN - Tags: CIVIL UNREST MILITARY TRANSPORT)

A U.S. military camera-equipped surveillance balloon flies over a village next to the mountain ridges as seen from the window of a Canadian helicopter transporting U.S. troops and workers to different U.S military bases in Kunar province in eastern Afghanistan September 19, 2011. REUTERS/Erik De Castro (AFGHANISTAN - Tags: TRANSPORT CIVIL UNREST CONFLICT MILITARY)

A U.S. Air Force AWACS surveillance aircraft comes in for a landing at the Royal Air Force base at Akrotiri in Cyprus March 20, 2011. Western forces hit targets along the coast of Libya on Saturday, using strikes from air and sea to force Muammar Gaddafi's troops to cease fire and end attacks on civilians. REUTERS/Andrew Winning (CYPRUS - Tags: MILITARY POLITICS)

LIBYA-AWACS/ - Diagrams and factbox explaining NATO's AWACS surveillance aircraft. RNGS. (SIN05)

A flight deck crew member guides an E-2C Hawkeye as it lands on the U.S. Navy's USS George Washington aircraft carrier during joint military drills between the U.S. and South Korea in the West Sea November 30, 2010.The nuclear-powered USS George Washington, which has 75 warplanes and a crew of more than 6,000, is taking part in around-the-clock drills in waters west of the Korean peninsula but well south of the sea border disputed by the North. REUTERS/Kim Kyung-Hoon (SOUTH KOREA - Tags: POLITICS MILITARY)

BRITAIN/TARANIS - Illustrated factbox on the Taranis Unmanned Combat Air Vehicle (UCAV) which was unveiled by the British Ministry of Defence on Monday. RNGS. (SIN03)

German Bundeswehr army soldiers launch an unmanned drone "KZO" aircraft in the German camp in Kunduz April 29, 2010. REUTERS/Fabrizio Bensch (AFGHANISTAN - Tags: MILITARY CONFLICT)

A Heron TP, also known as the IAI Eitan, surveillance unmanned air vehicle (UAV) flies during an official inauguration ceremony at Tel Nof Air Force Base near Tel Aviv February 21, 2010. An Israeli air force officer said the Israeli-made drone is larger than any other drone and can fly at higher altitudes, while carrying more weight including advanced technological systems. The officer said the drone's main advantage was its longer flying time, estimated at 20 hours. REUTERS/Gil Cohen Magen (ISRAEL - Tags: TRANSPORT MILITARY)

Israeli soldiers look at an IAI Eitan, also known as the Heron TP, surveillance unmanned air vehicle (UAV) on display at Tel Nof Air Force Base near Tel Aviv February 21, 2010. An Israeli air force officer said the Israeli-made drone is larger than any other drone and can fly at higher altitudes, while carrying more weight including advanced technological systems. The officer said the drone's main advantage was its longer flying time, estimated at 20 hours. REUTERS/Gil Cohen Magen (ISRAEL - Tags: TRANSPORT MILITARY IMAGES OF THE DAY)

An operator checks the computer system of a Chinese-made Unmanned Aerial Vehicle (UAV), which can be carried by a soldier, one day before the opening of the 7th China International Aviation & Aerospace Exhibition, or Airshow China 2008, in the southern Chinese city of Zhuhai November 3, 2008. About 600 exhibitors with more than 60 aircraft, representing 35 countries and regions, have registered to take part in the show. REUTERS/Bobby Yip (CHINA)

A U.S. soldier stands guards in front of U.S. Air Force U-2 spy-plane at the Air Power Day at the U.S. airbase in Osan, about 60 km (37 miles) south of Seoul, October 6, 2007. The Air Power Day event featured aircraft displays from South Korea and U.S. air forces as well as Patriot missile system and security forces equipment. REUTERS/Han Jae-Ho (SOUTH KOREA)

A journalist (front) is flown alongside a German police gyrocopter 'MT-03' during a test flight near Schoenhagen airfield, south of Berlin August 20, 2007. The gyrocopter, which will be used by police for traffic control and searches, is less expensive than a conventional helicopter. REUTERS/Hannibal Hanschke (GERMANY)

A soldier holds the drone Aladin of the German armed forces Bundeswehr during a demonstration at the exercise area of Munster about 80 km south east of Hamburg June 20, 2007. REUTERS/Christian Charisius (GERMANY)

U.S. President George W. Bush (R) and Homeland Security Secretary Michael Chertoff (C) listen to a briefing from Major General Mike Kostelnik (L) about a Predator Drone used in patrolling the Mexican border in Yuma, Arizona, April 9, 2007. Bush visited the area to highlight his immigration reform plan. REUTERS/Jason Reed (UNITED STATES)

Senior Airman Nicholas Nickert guards a United States Air Force E-8C Joint Surveillance Target Attack Radar System (JSTARS) aircraft at Hickam AFB, on Oahu, Hawaii on November 18, 2004. The JSTARS is a US$250 million spyplane designed to let commanders identify ground targets in all weather conditions. This aircraft is one of two that will be used in Resultant Fury, a marine strike demonstration scheduled for November 22-23, 2004 over the Pacific Ocean. REUTERS/Pascal Pink MB/JDP

Senior Airman Herbert Padgett guards United States Air Force jets at Hickam AFB, on Oahu Hawaii November 18, 2004. The E-8C Joint Surveillance Target Attack Radar System (JSTARS), seen in foreground, is a $250 million (USD) spyplane designed to let commanders identify ground targets in all weather conditions. This aircraft is one of two that will be used in Resultant Fury, a marine strike demonstration scheduled for November 22-23, 2004 over the Pacific Ocean. REUTERS/Pascal Pink MB

U.S. ambassador to South Korea Thomas Hubbard makes a speech in Seoul March 12, 2003. The U.S. envoy to South Korea said on Wednesday North Korea's decision to restart a nuclear reactor and buzz a [U.S. spyplane were "worrisome"] events that added urgency to the need for an effective approach to the North.

U.S. ambassador to South Korea Thomas Hubbard makes a speech in Seoul
March 12, 2003. The U.S. envoy to South Korea said on Wednesday North
Korea's decision to restart a nuclear reactor and buzz a U.S. spyplane
were "worrisome" events that added urgency to the need for an effective
approach to the North. REUTERS/Rhee Dong-Min

KKH/RCS

A South Korean tank takes part in a military exercise near the
demilitarized zone which seperates the country from communist North
Korea in Paju, about 50 km (31 miles) north of Seoul March 12, 2003.
The U.S. envoy to South Korea said on Wednesday North Korea's decision
to restart a nuclear reactor and buzz a U.S. spyplane were "worrisome"
events that added urgency to the need for an effective approach to the
North. REUTERS/Kim Kyung-Hoon REUTERS

KKH/

South Korean soldiers take a rest next to an armored vehicle during a
military exercise near the demilitarized zone in Paju, about 50 km (31
miles) north of Seoul March 12, 2003. The U.S. envoy to South Korea
said on Wednesday North Korea's decision to restart a nuclear reactor
and buzz a U.S. spyplane were "worrisome" events that added urgency to
the need for an effective approach to the North. REUTERS/Kim
Kyung-Hoon

KKH/RCS

South Korean armoured tank crew takes part in a military exercise near
the demilitarized zone which seperates the country from communist North
Korea in Paju, about 50 km (31 miles) north of Seoul March 12, 2003.
The U.S. envoy to South Korea said on Wednesday North Korea's decision
to restart a nuclear reactor and buzz a U.S. spyplane were "worrisome"
events that added urgency to the need for an effective approach to the
North. REUTERS/Kim Kyung-Hoon

KKH/RCS

A South Korean soldier mans a machine gun atop a tank during a military
exercise near the demilitarized zone which seperates the country from
communist North Korea in Paju, about 50 km (31 miles) north of Seoul
March 12, 2003. The U.S. envoy to South Korea said on Wednesday North
Korea's decision to restart a nuclear reactor and buzz a U.S. spyplane
were "worrisome" events that added urgency to the need for an effective
approach to the North. REUTERS/Kim Kyung-Hoon

KKH/RCS

South Korean soldiers stand on a tank during a military exercise near
the demilitarized zone which seperates the country from communist North
Korea in Paju, about 50 km (31 miles) north of Seoul March 12, 2003.
The U.S. envoy to South Korea said on Wednesday North Korea's decision
to restart a nuclear reactor and buzz a U.S. spyplane were "worrisome"
events that added urgency to the need for an effective approach to the
North. REUTERS/Kim Kyung-Hoon

KKH/RCS

A French Air Army fighter pilot jumps into the cockpit of a Mirage IV
jet before taking off for the Gulf at the military base of Istres,
Southern France, February 21, 2003. Two spyplane Mirage IV jets,
accompanied by two refuelling aircraft and a 70-strong support staff,
are expected in Gulf region to help locate and identify suspected sites
housing weapons of mass destruction in Iraq. REUTERS/Jean-Paul
Pelissier

jpp/

A French Air Army fighter pilot check his Mirage IV jet before taking
off for the Gulf at the military base of Istres, Southern France,
February 21, 2003. Two spyplane Mirage IV jets, accompanied by two
refueling aircraft and a 70-strong support staff, are expected in the
Gulf region to help locate and identify suspected sites housing weapons
of mass destruction in Iraq. REUTERS/Jean-Paul Pelissier

jpp/

French Air Army Mirage IV jet taxies past a refueling aircraft before
taking off for the Gulf at the military base of Istres, Southern France
February 21, 2003. Two spyplane Mirage IV jets, accompanied by two
refueling aircraft and a 70-strong support staff, are expected in Gulf
region to help locate and identify suspected sites housing weapons of
mass destruction in Iraq. REUTERS/Jean-Paul Pelissier

jpp/

A French Air Army Mirage IV jet takes off for the Gulf from the
military base in Istres, Southern France, February 21, 2003. Two
spyplanes Mirage IV jets, accompanied by two refueling aircraft and a
70-strong support staff, are expected in Gulf region to help locate and
identify suspected sites housing weapons of mass destruction in Iraq.
REUTERS/Jean-Paul Pelissier

jpp/JDP

A French Army fighter pilot gestures into the cockpit of a Mirage IV jet before to take off for the [Gulf] at the military base of Istres (Southern France), February 21, 2003. [Two spyplanes Mirage IV jets, accompanied by two refueling aircraft and a 70-strong support staff, are expected in Gulf region to help locate and identify suspected sites housing weapons of mass destruction in Iraq.]

A French Air Army fighter pilot check his Mirage IV jet before taking off for the [Gulf] at the military base of Istres, Southern France, February 21, 2003. [Two spyplanes Mirage IV jets, accompanied by two refueling aircraft and a 70-strong support staff, are expected in Gulf region to help locate and identify suspected sites housing weapons of mass destruction in Iraq.]

A French Army fighter pilot opens the cockpit of a Mirage IV jet at the military base of Istres in southern France February 20, 2003. [Two spyplanes Mirage IV jets, accompanied by two refueling aircraft and a 70-strong support staff, are expected in Gulf region to help locate and identify suspected sites housing weapons of mass destruction in Iraq.]

A French Army fighter pilot climbs into the cockpit of a Mirage IV jet at the military base of Istres in southern France February 20, 2003. [Two spyplanes Mirage IV jets, accompanied by two refueling aircraft and a 70-strong support staff, are expected in Gulf region to help locate and identify suspected sites housing weapons of mass destruction in Iraq.]

A French Air Army fighter pilot jumps into the cockpit of a Mirage IV jet before taking off for the [Gulf] at the military base of Istres, Southern France, February 21, 2003. [Two spyplanes Mirage IV jets, accompanied by two refueling aircraft and a 70-strong support staff, are expected in Gulf region to help locate and identify suspected sites housing weapons of mass destruction in Iraq.]

A French Air Army Mirage IV jet takes off for the [Gulf] from the military base in Istres, Southern France, February 21, 2003. [Two spyplanes Mirage IV jets, accompanied by two refueling aircraft and a 70-strong support staff, are expected in Gulf region to help locate and identify suspected sites housing weapons of mass destruction in Iraq.]

A U.S. Navy C-9 Skytrain (top) carrying the 24 EP-3E crewmembers taxis toward a sister VQ-1 Squadron EP-3E spyplane at Naval Air Station Whidbey Island, April 14, 2001. The crew, who survived the midair collision with a Chinese military jet near Hainan, China, on April 1 were released from detention on April 11 and were flown-in from Hawaii after two days of debriefings there. REUTERS/Anthony P.

APB/HB

A chartered aircraft carrying 24 U.S. air crew to freedom takes off from Haikou airport on China's Hainan Island April 12, 2001. The plane, carrying the crew of an EP-3 spy plane which made an emergency landing on Hainan on April 1 after a collision with a Chinese fighter, is bound for Guam.

PB

A chartered aircraft carrying 24 U.S. air crew to freedom takes off from Haikou airport on China's Hainan Island April 12, 2001. The plane, carrying the crew of an EP-3 spy plane which made an emergency landing on Hainan on April 1 after a collision with a Chinese fighter, is bound for Guam.

PB/CLH/

A chartered aircraft carrying 24 U.S. air crew to freedom takes off from Haikou airport on China's Hainan Island April 12, 2001. The plane, carrying the crew of an EP-3 sply plane which made an emergency landing on Hainan on April 1 after a collision with a Chinese fighter, is bound for Guam.

PB/CLH/

A chartered aircraft carrying 24 U.S. air crew to freedom takes off from Haikou airport on China's Hainan Island April 12, 2001. The plane, carrying the crew of an EP-3 spy plane which made an emergency landing on Hainan on April 1 after a collision with a Chinese fighter, is bound for Guam.

PB/CLH/

A chartered aircraft carrying 24 U.S. air crew to freedom takes off from Haikou airport on China's Hainan Island April 12, 2001. The plane, carrying the crew of an EP-3 sply plane which made an emergency landing on Hainan on April 1 after a collision with a Chinese fighter, is bound for Guam.

PB

A Continental airplane arrives at Haikou airport, prior to the detained U.S. crew boarding the plane and leaving China, April 12, 2001. They were held for the most of their time in China in a military guest house during their 12 days of detainment following the collision of their EP-3 spyplane with a Chinese jet fighter.

CMC/PB

Onlookers surround an SR-71 Blackbird spy plane as it is rolled out from a hanger at the Imperial War Museum in Duxford April 11, 2001, the first such plane to be exhibited on permanent loan outside the U.S. Chinese state media said today that the 24 crew from the detained U.S. EP-3E Aries II spy plane on the island of Hainan were due to be released.

RUS

U.S. Navy Lieut. Shane Osborne, the commander of the EP-3E spyplane that survived a midair collision with a Chinese military interceptor jet near Hainan Island, China on April 1, 2001, greets fans as he walks out to the mound to throw the ceremonial first pitch before the start of the Baltimore Orioles game against the Seattle Mariners at Safeco Field in Seattle, May 29, 2001. Fourteen of the 24 aircrew who were held hostage in China for 11 days before they were allowed to return to their homestation at Naval Air Station Whidbey Island on April 15, 2001, attended the Mariners game. REUTERS/Anthony P.

APB

U.S. Treasury Secretary Paul O'Neill (C) and Under Treasury Secretary designate John Taylor (R) chat before their bilateral meeting with Chinese Finance Minister Xiang Huaicheng (not pictured) during the Asian Development Bank (ADB) conference at the Hawaii Convention Center in Honolulu, May 10, 2001. The closed-door meeting involved the highest ranking officials from the two countries since the April 1, 2001 midair collision between the U.S. Navy EP-3E spyplane and the Chinese military interceptor jet. REUTERS/Anthony P.

APB/ME

Chinese Finance Minister Xiang Huaicheng (L) and Deputy Finance Minister Jin Li Qun (R) arrive for a bilateral meeting with U.S. Treasury Secretary Paul O'Neill during the Asian Development Bank (ADB) conference at the Hawaii Convention Center in Honolulu, May 10, 2001. The closed-door meeting involved the highest ranking officials from the two countries since the April 1, 2001 midair collision between the U.S. Navy EP-3E spyplane and the Chinese military interceptor jet. REUTERS/Anthony P.

APB/ME

UNDATED FILE PHOTO - Iraq demanded on November 3 the cancellation of flights by U.S. U-2 spy planes, shown in an undated file photo, in support of U.N. weapons inspectors and warned that they could be shot down by Iraqi anti-aircraft fire. The threat was contained in a letter from Iraqi U.N. envoy Nizar Hamdoon to the head of the U.N. special commission in charge of scrapping Iraq's weapons of mass destruction, Richard Butler.

IRAQ UN