From Civil War-era battlefield balloons to unmanned, jet-powered drones, the best view of the enemy has always been from above. Here’s a look at aerial surveillance technology over the past 200 years, with contributions from Andrew Hammond, historian and curator at the International Spy Museum in Washington, D.C.

In the early 1790s, the French first experimented with using hydrogen-filled balloons for battlefield reconnaissance. The balloons didn’t actually fly over enemy lines; they were tethered to the ground by cables. The baskets held two soldiers: one manning a telescope and the other signaling observations to the ground with flags. The French balloonists formed the world’s first air force in 1794 called the Compagnie d'Aéronautiers.

“Before that, the only way to get a sense of your enemy’s position was by sending in cavalry reconnaissance,” says Hammond. “Up in a balloon, you could see maybe 50 miles on a clear day. It gave you tremendous advantages to see your enemy from that height.”

At the outbreak of the Civil War, the American inventor and showman Thaddeus Lowe staged a balloon demonstration on the National Mall that convinced Abraham Lincoln to employ tethered balloons in the Union Army. The largest Union reconnaissance balloon, the Intrepid, could carry five people, including a telegraph operator to relay information about Confederate positions.

In the 1880s, a British meteorologist named Douglas Archibald experimented with large canvas kites for studying wind velocity. He also rigged a camera to the kite and activated the shutter through a long cable attached to the kite’s string. Archibald’s aerial photographs were some of the earliest ever published and caught the attention of an American army corporal named William Eddy.

While fighting in the Spanish-American War of 1898, Eddy built his own version of Archibald’s kite-mounted camera and used it to snap bird’s-eye photos of enemy positions. Although photography existed during the Civil War, it was Eddy’s kite that took the first military aerial surveillance photos in history.

Carrier pigeons or homing pigeons played a vital role in World War I communications. They carried SOS bulletins from marooned sailors, relayed orders to tank officers and transported coded messages from covert spies.

Pigeons also took aerial photos. Or tried to.

In 1907, a German pharmacist named Julius Neubronner patented a pigeon-mounted camera and used his invention to create whimsical postcards featuring photographs taken “on the wing.” In World War I, the German army experimented with avian photographers, which were more discreet than spy planes.

“They literally strapped a camera to pigeons and would send them up over the trenches in France,” says Hammond, but the photos were blurry and too difficult to interpret. “The history of intelligence and espionage is filled with many more attempts that failed than ones that worked.”

The CIA also conducted tests of a lightweight pigeon camera to snap close-range surveillance photos of targets, but the birds proved too hard to control.

Airplanes first went to war during World War I, but before those early aircraft were outfitted as fighters and bombers, they were used for reconnaissance. The two-seater planes carried a pilot and an observer, who sketched the layout of enemy troops with the help of binoculars.

Then came cameras. The Eastman Kodak company in America designed some of the first aerial cameras to be hard-mounted on the side of British-made de Havilland DH-4 aircraft. Other World War I cameras could snap photos through a hole in the cockpit floor. At its headquarters in Rochester, Kodak ran the U.S. Aerial Photography School, an intensive training program for American soldiers tasked with developing surveillance photos under battlefield conditions.

By World War II, surveillance planes started carrying a portable onboard darkroom for developing and analyzing aerial photos in near real-time. During the Cold War, the KGB made it almost impossible to collect intelligence on the ground in the Soviet Union, so America’s spy agencies turned to the skies.

“Necessity is the mother of invention,” says Hammond. “That’s why you get the development of the U2, which could fly at 70,000 feet, more than twice the cruising altitude of today’s commercial jets.”

The U2 was equipped with a Hycon 73B camera, capable of capturing details as small as 2.5 feet wide from dizzyingly high altitudes. In 1962, a U2 captured images of Soviet nukes in Cuba, sparking the Cuban Missile Crisis.

For the U.S. and the Soviet Union, the space race was about more than being the first to reach the moon. The nations' intelligence agencies were also racing to get the first spy satellites in orbit.

“Satellites are commercial now, but back then they were mainly for defense and military purposes,” says Hammond.

In the late 1950s, the U.S. Air Force launched a program called Discoverer dedicated to collecting scientific data with satellites. At least that was the cover story. In reality, it was a secret spy program called Project Corona. The American spy satellites returned their first aerial images of the Soviet Union in 1960.

The heavy hitter of the late Cold War era was the HEXAGON KH-9, an American spy satellite that could capture images of objects smaller than two feet across from up to 100 miles above the earth’s surface. Before digital images could be transmitted from space, the KH-9 would jettison “buckets” of exposed film that parachuted down into the atmosphere over Hawaii, where they were snatched in mid-air by Air Force jets.

One of the most buzz-worthy gadgets at the CIA Museum is the insectothopter, a covert listening device camouflaged as a realistic looking (and flying) dragonfly.

The CIA built the device in the 1970s after ditching an earlier effort to build a bumblebee-shaped gadget. The insectothopter’s translucent wings were powered by a tiny gasoline engine and it flew fast enough to cover two football fields in 60 seconds. An operator controlled its flight using a laser beam, which also transmitted audio captured by the bug’s tiny microphone.

Unfortunately, the insectothopter was never operational because it was easily blown off course by gusts of wind stronger than 5 mph.

UAVs or “unmanned aerial vehicles” made their debut in World War I with the Aerial Target, a British remote-controlled airplane. As its name implies, the Royal Air Force used the UAV as target practice for British dogfighters in 1917.

For World War II, the RAF upgraded its UAV fleet to the Queen Bee, a reusable and returnable training target for anti-aircraft gunners. The Queen Bee, built by de Havilland, used a radio-controlled servo to manually operate the aircraft’s rudder and elevator controls. Some historians credit the bee-themed UAV with coining the word “drone.”

The first jet-powered drones were deployed in the Vietnam War as part of a secret American reconnaissance program. The AQM-34 Ryan Firebee, which ran more than 34,000 surveillance missions during the war, was equipped with radar-absorbing blankets and anti-radar paint to give it stealth capabilities. In addition to tracking Viet Cong positions and spotting targets, the Firebee was also used to scatter propaganda leaflets behind enemy lines.