as the sophistication of time lapse photography has increased, so we have been able to show that plants can be as competitive and as aggressive as many an animal. and it was the mastery of time lapse that allowed us to make a series called "the private life of plants." condense three months into 20 seconds, and the desolation of winter quickly warms into the riot of spring. speed a week into a minute and you can sense the urgency with which the ground-living plants race to unfurl their flowers. of all the woodland plants the humble bramble is one of the most aggressive. it waves its shoots agitatedly from side to side as if feeling for the best way forward. the invading stem's backward pointing spines give it the grip it needs to climb over almost anything that stands in its way. it can advance as much as three inches in a day. now, digital cameras allow us to see how a shot is developing while we are still taking it instead of having to wait till it was finished as we used to have to do with film cameras. and we can also use computers attached to small motors to move a camera in between exposed frames, so that the camera can, in fact travel alongside a plant. using this new technology, it became has possible to condense the arrival of spring in a woodland into a few seconds. but the wonderful thing about wildlife filmmaking is that, no matter how much you've seen and filmed there's always going to be something to surprise you. i remember back in 1994, we were filming nepenthes rajah, the largest pitcher plant in the world growing up in the mountains of borneo. and i made an assumption about how it obtained its nitrogen fertilizer. i guess this one contains, oh, two or three pints of liquid. it's so big that it catches not just insects but even small rodents. and one was recorded that had in it the body of a drowned rat. so if ever there was a carnivore among plants this is it. but i was wrong. in 2010, scientists discovered that the plant gets its nitrogen in a quite different way and we couldn't resist going back to see if we could find out what the truth was. mount kinabalu in sabah is home to many rajah pitcher plants. they certainly seem to attract insects that fall into their bowls just as other pitchers do. but they also have larger visitors. a tree shrew. it's licking the underside of the lid where the pitcher secretes nectar, with which it lures visitors. but even though its backside is hanging over the bowl it doesn't seem to be in any danger of falling in and drowning. so, what's going on? it leaves a clue -- a dropping. so, the pitcher is a tree shrew toilet. the tree shrew feeds by licking the secretions from the pitcher plant's lid and the pitcher plant gets its fertilizer by collecting the tree shrew's droppings. [ helicopter whirring ] wildlife cameramen are always trying to film some piece of animal behavior that no one has ever seen before and aerial photography enabled them to do just that. in the early days, we occasionally managed to get up in a small plane to get a shot of the landscape. but the plane vibrated so much that you couldn't use long lenses to get close-ups of animals, and if you went low, the roar of the engine frightened them. so we tried other forms of aerial transport. balloons were a little quieter but they took you where the wind blew them not where you wanted to go and getting steady shots was still difficult. it wasn't until the invention of a kind of mount that could hold the camera almost miraculously free of vibration that it was possible to use the long lenses necessary in order to film animals from a height when they didn't even know you were there. it's almost impossible to follow a wild dog hunt at ground level through the treacherous swamplands of the okavango delta in africa. but the "planet earth" series used a helicopter with a new stabilizing mount that kept the camera vibration-free and you could get close-ups from so high up that the animals below didn't know you were there. man: there, there, there there it goes, there it goes they are racing, they are racing, they race. three or four dogs all spread out. they are pulling up fast. tighten up, tighten up as much as you can. attenborough: by intercutting aerial shots and shots from the ground, we could show how the dogs worked as a team with fresh animals joining the hunt to harry their prey and cut off its escape. this new perspective gives us the big picture, helping us to understand behavior we could only see fragments of before. man: stay with him he's almost got him. so, he's heading towards the water. oh, the croc's gonna get that impala. attenborough: so, now we have the techniques to film almost anything on land, or in the sea or in the air. but to get pictures of animals that lived in the past you have to recreate life. in the early days, our attempts were pretty crude. we used solid models of extinct fish placed in swamps to show the arrival of amphibians on land. we moved on to line drawings of dinosaurs, and i even appeared alongside one. it's easy to imagine some 12 foot species of a pelycosaur like dimetrodon, lying basking on the rocks in the early morning sun. and then we began to animate the drawings but not very realistically. it would take the advent of computer animation to make them move like real animals. we wanted to use these new computer techniques to bring to life a moa the giant extinct ostrich-like bird of new zealand. first of all, i had to walk into a woodland glade holding a moa bone. then what would happen would be that, that bone would be suspended i'd take my hands away and all the rest of the bones and the skeleton would appear from nowhere, materialize to form the complete skeleton. so, i had to walk in hold the bone, then actually take my hands away and let it drop which seemed a silly thing to do. but electronic trickery made it stay there and then added the rest of the bones of the moa's skeleton. it had just three toes. its pelvis and its spine lead up to an extraordinarily long neck. this bird stood over six feet -- two meters -- tall. but then we wanted it to walk away and so what the computer expert got us to do was to imagine where it was gonna stand and then conceal ourselves in the vegetation, each of us holding a bit of fishing line attached to a branch. and with our computer expert conducting us as though he was conducting an orchestra, the moa came in, this branch was brushed away and then it reached up and pecked another leaf, and the leaf moved and then it moved away and the bushes moved. it was really quite convincing. the first human settlers on these islands saw these giants alive and called them moas. among them were the tallest birds that ever existed, that weighed over 200 kilos, 400 pounds. so, now we could recreate extinct creatures whenever we liked, in their entire, full-color, animated glory. a succession of technological advances has certainly changed the way we make natural history films. these days with every year that passes, we seem to get more and more equipment. longer lenses, more electronic bits of kit. but in the end often the most memorable shot comes from just one camera and one person with a deep understanding of the natural world. to film a wild snow leopard was once the ultimate challenge for a wildlife cameraman. doug allan went to the himalayas to attempt to do what so many cameramen before him had tried but failed. i guess this is where you could say it really starts. we're up here in snow leopard country. you look around, and anywhere, anytime, you might just see it. these are big, big mountains and there are not many snow leopards. attenborough: nevertheless, doug took to his hide and waited. [ exhales ] this is tedious stuff. not a sign. if you got just, just a little bit of hint, a wee bit of a sighting now and again, your spirits would be lifted but right now i'd swap a little bit of this animal's charisma for a little bit more visibility. attenborough: and things didn't improve, even after two weeks. yeah, of course it's boring. it's boring as hell. [ chuckles ] attenborough: after seven weeks of patiently sitting and watching these distant shots are all doug managed to film so he had to return home empty handed. the following winter cameraman mark smith took up the challenge, and tried a different location this time in pakistan. smith: we just got a lot of snow, and we'll be able to track the snow leopard -- and so we'll have a lot better chance of filming it so it's just fantastic. attenborough: after that promising start things didn't go so well for mark. he and the crew spent a fruitless month trudging through the snow. mark spent all christmas in the mountains with no sign of a snow leopard, but it was a much happier new year. we just got -- we just got a report there's a snow leopard up on the ridge. we were too low where we were before so it's just trying to get some height to get a better view of it. attenborough: finally, mark was rewarded with his first ever glimpse. smith: i looked up onto the ridge i could see this leopard-shaped rock which i've seen a million times before and i looked through the binoculars and it was a leopard just sat there it was perched, like just on top of the rock, and it looked down at us and it sort of sat down in a sort of sphinx-like posture. attenborough: a few days later mark's patience paid off. there was not just an adult female, but with her a one year old cub. overall mark spent eight months in pakistan and his dedication enabled him to document the most intimate moments of a snow leopard's life -- including a hunt. silently she positions herself above her prey. the revelations brought by wildlife films today were beyond my imagination when i set out 60 years ago. they have transformed not only our understanding of the natural world but our attitudes towards it. "nature's" three-hour series continues... through the lens of attenborough's remarkable body of work, we look back at some of the greatest riddles solved by science. attenborough: what forces could possibly have raised the sea bed to these heights? and reveal how those discoveries transformed our view of the living world. this is the secret language of dna. this is the book of life. don't miss a single moment. now you can watch "nature" online. go to pbs.org to screen complete episodes from this season and seasons past. visit "nature" online for production updates from the field. well, here we are on the alaska coast. go behind the scenes with our filmmakers. we also used a borescope lens and that allowed us to put the lens right into a flower. and get connected with "nature's" online community. all at pbs.org. "nature" is made possible in part by... leave it untouched by your presence capture its image and preserve it forever. canon -- living and working together to appreciate today and care for tomorrow. the corporation for public broadcasting... and by contributions to your pbs station from viewers like you -- thank you. to order this three-part "nature" series on dvd and blu-ray call 1-800-336-1917. to learn more about what you've seen on this "nature" program, visit pbs.org. available now on shoppbs downton still stands. i'm looking forward to all sorts of things. what?! no one must know! i'm warning you... to order, visit shoppbs. also available on itunes. 5,4,3,2,1... when you want to go above. it is a major exploratory expedition or reach beyond. it was exciting and mysterious when you want to dive deep. words cannot describe how amazing this is or push the limit i am constantly awestruck... nova. only on pbs. er man: the hvi is on the move. narrator: drones. these aerial robots are replacing manned planes. they're revolutionizing warfare by allowing us to see and kill from half a world away. and they're making science fiction a reality. now, with unprecedented access to drone scientists, engineers, and pilots, nova reveals the technologies that make drones so powerful and the breakthroughs that are leading us into the future. will drones soon replace even the most sophisticated manned planes and become a part of our everyday lives? it started out as a toy for my dogs to chase. rand paul: the worry is that we'll have 30,000 drones crisscrossing the sky accumulating all this information. narrator: they generate opposition both overseas and at home. i speak out on behalf of the rule of law. narrator: now, enter a new chapter in aviation history as nova takes you inside the "rise of the drones." three, two, one... (beeping) major funding for nova is provided by the following... supporting nova and promoting public understanding of science. and by the corporation for public broadcasting. and by contributions to your pbs station from: additional funding from: inspiring tomorrow's engineers and technologists. and millicent bell through: narrator: this is the ultimate melding of man and machine. the u.s. has more than 2,300 manned fighter planes, and pilots like matt mcdonough have long been our heroes. mcdonough: the best fighter pilots that i've seen are the ones that can make a quick decision when things are happening very quickly. narrator: but a revolution is underway as manned planes are replaced by drones. are we approaching a time when movies like the terminator become our reality? oh god, it's the machines. they're starting to take over! narrator: a time when machines fly, think, and even kill on their own. drones are aerial robots that carry visual sensors, navigation systems and sometimes even weapons. they come in all shapes and sizes and go by a variety of names. david deptula: the united states air force uses the term "remotely piloted aircraft." they are also known as unmanned aerial vehicles or, as the media likes to call them, drones. narrator: already the pentagon relies on a family of more than 10,000 drones, usually to spy but sometimes to kill. small enough to fit in a soldier's backpack, the three-foot-long raven is the most widely used spy drone in the world. the stealthy sentinel provided crucial intelligence in the raid to kill bin laden. the killer predator has flown thousands of missions since 2001 and the giant global hawk can stay aloft and spy for up to 35 hours. the military uses drones to support troops on the ground. the cia maintains a covert drone program to find and target individuals. the government claims drones have helped to eliminate up to 70% of al qaeda's top leadership. they have been so effective, the air force predicts nearly a third of its attack and fighter planes will be drones within a decade. planes can fly longer, they can pull more gs, they can be more precise when they bomb if a human is not in the cockpit. narrator: we're entering a new era when the supremacy of even the most advanced planes is being challenged as engineers take the pilot out of the cockpit. holloman air force base in southern new mexico is the largest air force training base for operators of remotely piloted aircraft. chad: my name is chad, and i'm a captain in the united states air force. for security reasons we've been asked to cover our last names to prevent us from potentially becoming a target of any kind. narrator: captain chad has flown remotely piloted aircraft in combat for three years and now teaches pilots to fly the world's most famous killer drone. it's known as the mq1, or more commonly, the predator. the predator has changed warfare, but it's just a hint of what's to come. deptula: where we are in terms of unmanned aerial vehicles is about the same place we were with biplanes right after world war i. we are at the very very early stages of realizing what the potential of unmanned aerial vehicles are. narrator: unlike complex fighter planes that are engineered for speed and agility, the predator is built for endurance, so it needs to be light and efficient. chad: it's the weight of a pick-up truck or so, about 2,000 pounds. and it's balanced pretty evenly on the wheels. with one hand here i can lift it up and set it back down. narrator: the propeller-driven predator cruises at only 84 miles per hour, and its four-cylinder engine burns about 300 times less fuel than a fighter jet. chad: i can't say exactly how long it can stay up, but it is possible to stay up over 24 hours. narrator: a typical fighter plane can only fly for about two hours without refueling, and short, angled wings keep it fast and maneuverable. but the predator hovers five miles up, often in uncontested airspace, and its long wings maximize lift. chad: as you can see it's got some flex to it. narrator: with no pilot to protect a remotely piloted aircraft is much lighter and simpler than a manned plane. on a fighter the pilot's support equipment and ejection system alone weigh as much as a predator, which in place of a cockpit has a satellite control system. chad: it's essentially the brains of the aircraft that gives us the ability to communicate, control, to keep link with the aircraft and navigate it. narrator: the predator's sensor ball carries daylight and infrared cameras. chad: we can easily make out people from five, six miles away. narrator: the sensor ball also guides the predator's two hellfire missiles. chad: from right here we fire the laser and the laser spot hits the ground, and then once we fire the missile, this is the seeker, so this seeker will find that laser spot on the ground and travel to that spot, giving us a very precise capability of employing weapons. narrator: when conducting missions remote pilots work out of small trailers on the ground. they control the predator by satellite. this link is what makes it possible to take the human out of the cockpit and fly from virtually anywhere on the planet. chad: it's tight, about the size of a normal shipping container. a shift can be anywhere from two or three hours up to eight or more hours depending on the situation. narrator: from trailers like this, pilots of the predator and its larger cousin, the reaper, have killed thousands of individuals since 2001. in this clip from iraq a predator pilot sees two insurgents firing mortars towards a coalition airbase. he tracks them and finally shoots. woman: splash. narrator: the pilot's role is to support troops on the ground and go after threats while trying to minimize civilian casualties. we got a new altimeter for you. narrator: with such high stakes, pilots like chad need ongoing training. today, he'll be flying the reaper in an exercise 50 miles away in the new mexico desert. man: all right, greg, you're going to be my hvi. i have... shadow 1 station is going to be watching you. narrator: a group of former soldiers working for a company called rally point will run an exercise in which chad will hunt down insurgents in a mock village. we'll strike you there and once you die stay there, drive... narrator: two will play insurgents and one will be a soldier on the ground communicating with chad. chad: have to take off now, so we are going to push the throttle up. and there, we're up in the air. narrator: the training mission offers a rare glimpse into the mechanics of how the u.s. uses drones to support troops and prosecute its war on terror. the goal is to make it as realistic as possible so pilots can avoid mistakes when in battle. they should be checking in here probably in the next 20 minutes ore so. it's going to be an mq-9 a reaper. if they're at 25,000 feet, which they generally work, we're not going to be able to see them at all. narrator: it takes about half an hour to reach the mock village. drones like the reaper can fly on their own using autopilot and pre-set gps locations. but the air force still keeps human hands on the controls at all times. people have this concept of either, "it's a manned plane and the pilot's doing everything," or, "it's an unmanned plane and it's something out of the terminator movies." the reality is it's in the middle right now for both the manned and the unmanned planes. our mind tries to put it in terms of robot or human but the reality is a mix. narrator: as chad pilots the reaper, his sensor operator, jay controls the cameras and lasers. on the ground, the fake insurgents enter the village as the reaper hovers miles above. bones 3-4, rally 2-0 say status. rally from bones 3-4. we have eyes on the target. narrator: chad gets direction from the soldier whose handheld receiver and computer allow him to see what chad sees. chad's call sign is "bones." the soldier goes by "rally." chad: rally from bones we have two packs moving around inside the northwest corner of the compound. bones 3-4 from rally 2-0 continue to shadow. narrator: the soldier directs chad and jay to follow an hvi or high value individual dressed in black. chad: rally from bones 3-4. looks like the one individual wearing black is now getting on the motorcycle and departing the group. narrator: depending on the situation the decision to kill comes from an intelligence officer who could be anywhere, a battle commander on the ground, or sometimes the pilot. bones 3-4 from rally 2-0. looks like that personnel is stopping. chad (on walkie talkie): bones 3-4, that's what we've got up here. would like to go ahead and prosecute. nine line, bravo, one. copy, master arm. narrator: the sensor operator targets using the laser. chad: this will be a run against the target under our crosshairs. ten seconds release. sensor, are you ready? copy. chad: three, two, one, rifle. bones 3-4, weapons away. 25 seconds time of flight. narrator: the predator uses laser-guided hellfire missiles. deptula: the weapons that can be used operate with an error distance of less than nine feet. you can put a weapon through a window-sized opening with ease. chad: five, four, three, two, one... splash. rally, it's bones, we have a splash. stand by for bda. bones, rally-- looks like a good splash. copy, lasers off and master arm is now safe. narrator: the efficiency of having a single craft able to find, follow and eliminate a target like this in real time represents a revolution in warfare. deptula: let's go back to the middle of the last century. during world war ii, it took on the order of months to assemble intelligence from a variety of different sources whether it be airborne or on the ground to assimilate that information and then determine what targets might be hit. then it took hundreds of aircraft and literally thousands of bombs to go out and attack a target using that information that had been developed over a period of months. today, with the capabilities all wrapped up into one vehicle, the predators and the reapers in particular, you can accomplish that "find, fix, finish" cycle in a matter of single-digit minutes. narrator: before the predator, the military had to design separate aircraft for intelligence-gathering and attack. reconnaissance was key and after world war ii engineers built ultra-sophisticated spy planes. they went faster and higher than ever before to make sure the pilots and the information they gathered didn't fall into enemy hands. man: the sr-71 was triple sonic. in other words, it could go over mach three. max recorded altitude was 85,200-some feet. and there's several of us that have gone higher than that. narrator: pilot tony bevacqua is one of a select group of men to fly the sr-71 a titanium spy plane built during the height of the cold war that could take photos of the ground with 12-inch resolution from 90,000 feet. literally faster than a rifle bullet even missiles were too slow to catch it. bevacqua: i was the first person in the sr-71 to get shot at and it was over hanoi. you got an airplane that's going 2,200, 2,300 miles an hour and it's very, very difficult to even come close. they figure that the missile exploded about a mile below me and we're in and out of there in no time. (laughing): thank god. narrator: the cost of such speed was that the sr-71 needed to be refueled every two hours. but there was a slower alternative called the u-2. bevacqua is one of only 12 pilots to have flown both operationally. bevacqua: i was very proud of being a u-2 pilot because of what we have done and what we're still doing. it's just a magnificent platform and does excellent reconnaissance. narrator: still widely used today nearly 60 years after its introduction pilot endurance limits u-2 flight time to 12 hours. mcdonough: it's pretty demanding on their bodies. they have to wear a special high altitude suit for it. and then it wipes them out for a good couple of days. it fatigues them quite a bit to go that high. narrator: manned spy planes are not only limited by human endurance they also bring the risk of pilot loss. in 1960, bevacqua's friend francis gary powers, was shot down while flying a u-2 over the soviet union. reporter: it was a propaganda field day for the russians. narrator: powers' cover story was that he was on a meteorological flight. becqua: frank powers tried to say it was a weather flight, but there's miles of film. and so it was easy to discern what he was doing. reporter: and khrushchev denounced the united states with every epithet in his vocabulary. he summarily rejected all attempts of the west of reconciliation. narrator: powers was imprisoned in russia for more than two years, creating a major international incident and clearly demonstrating the need for unmanned spy planes. reporter: it was a development from the pilotless aircraft principle. guidance was by radio from an accompanying aircraft. after reaching altitude... narrator: as early as world war ii once at altitude airplanes could be controlled by radio signals after the pilot bailed out. but for decades afterwards before gps, drones were limited by primitive autopilots and navigation systems. in the '60s and '70s drones crashed constantly, including the most advanced unmanned aerial vehicle, or uav: the aquila drone that averaged a crash every 20 hours. singer: it was a small propeller drone that would fly over the battlefield and gather information and beam it back to you. the problem is, back in the '70s the technology wasn't ready yet. it was a billion-dollar program by the time they got just a couple of prototypes. man: i was frustrated that the u.s. could not make uavs really work. narrator: abe karem is the father of the predator. karem: this is one of two small uavs built in my garage between 1980 and 1983. i was borrowing $18,000 a year from family, that's all we had. everything was built with the lowest possible technology. we were trying to show that if you design the best you can then you are going to get performance by design. narrator: on his first prototype the albatross, karem placed the engine and propeller in the rear so they wouldn't interfere with the delicate sensors up front. and the inverted tail is also still visible on its famous descendant. karem: down-deflected tails are there to protect the prop, so when it tilts back, it's hitting the skids and not hitting the propeller. narrator: an ex-fighter jet engineer today karem designs and builds planes at his company in california. in the '70s, when he started working on drones, he realized that without a pilot in the seat, a whole new world of design possibilities opened up. other unmanned aerial vehicles of the time were still too closely modeled on manned aircraft. i said "i don't like what i see." "i'm not going to take the engine, i'm not taking the prop, i'm not taking the landing gear, i'm not taking the computer." narrator: karem believed that efficiency and lightness were the key to creating an affordable, high endurance uav so first he gave his craft long wings to prioritize lift over speed. karem: when you want to be efficient, you want to be like the soaring birds with very long-span wings. the albatross is the best gliding bird; it has 20 times more span than the chord. and my albatross, the uav albatross, was close to that. narrator: karem built the albatross from scratch in his garage. he modified a go-kart engine to burn only 1/10th of a gallon of fuel an hour. and albatross soon evolved into amber a 15-foot-long, 28-foot-span uav with 38-hour endurance. karem relied on seed money from darpa-- the defense advanced research projects agency. its early investments in artificial intelligence and other technologies led to countless civilian uses and made modern uavs possible. man: in the 1970s and 1980s with significant darpa impetus and some darpa funding a variety of new technologies emerged, including the global positioning system, long-range data links, lightweight computer equipment and composite materials, as well as satellite communications and digital flight controls. the albatross, the amber were the harbingers of the modern era of uavs. karem: we were a total team of three people. and we proved a lot of what we wanted to prove. the secretary of the navy and the head of darpa, they said "okay, you fly 500 hours, how many are you going to crash?" we ended up not crashing any in the 500 hours we did for the military. narrator: karem's amber prototype never went into full production, but after a number of incarnations, by the mid '90s his design became known as the predator. man: do not handle the missile by the strikes wings, fins, seeker head rocket motor, nozzles, umbilical connector, or housing during loading to prevent damage to equipment and/or injury to personnel. karem: my uavs were not meant to be armed. it was really built for the cold war when we had the big tactical challenge with so much artillery on their side and so much artillery on our side. narrator: with two large armies facing off uavs could be used for espionage, but not attack. then, after 9/11, america started targeting individuals. karem: now we are fighting non-state enemies, so it starts making sense to arm the uav which is not my intention in the beginning. narrator: in october 2001, an armed predator changed warfare forever. deptula: i was the commander of the air operations against afghanistan where we actually used for the first time a weapon off the mq-1 predator. the advantages were enormous an order of magnitude beyond where remotely piloted vehicles had been just ten years prior in desert storm. narrator: since this initial strike, drones have proven so effective that the air force is now training more remote pilots than manned fighter and bomber pilots combined. so play on the scenario. narrator: at holloman air force base in new mexico, instructor major jason teaches this new generation of pilots. adam zero three, loud and clear. narrator: the stakes are high when operational so they begin on video simulators. he invents practice scenarios programmed using x-box video game controllers. adam zero nine from viking zero one, you are cleared hot. stuff that we can't do in the real plane, i can do anything here. the world's whatever i want it to be. student: three, two, one, rifle. jason: it's a controlled environment and we really want them to learn here so that when they do go operational, you know they've already made all those mistakes. student uh, pilot, it doesn't look like i ever turned the laser on so i don't know where the missile went. jason: how did that happen? if that would have happened in the real world, that would be a really, really bad day. narrator: unlike fighter pilots who train for a minimum of two years remote pilots learn to fly their increasingly automated drones in less than one. cummings: the faa did a study recently that showed that pilots with real flight experience in manned aircraft are actually worse uav pilots than those that have no flight experience and really come in off the street. you actually bring in a skill set that you don't need and a set of expectancies that you shouldn't have when you're flying a uav if you came from a manned aircraft. so the air force is taking officers off the street with no flight training and putting them through the program, and they've been very successful. jason: they come here, they never went to pilot training like i did. they're here for a few months and then they have to go operational, so it happens real fast. man: rifle time of flight 15 seconds. narrator: and when pilots go operational despite being half a world away from the action, it all feels very real. jason: copy, splash. chad: it's not like a video game at all. there's no reset button, there's no turning it off. narrator: in real strikes, like this one in iraq, technology actually allows drone pilots to see more than manned pilots ever have. chad: because we have such a long motor time there's potential to have eyes on the target that we are going to blow up for hours ahead of time. then we employ on it-- strike the target. and then stick around for another few hours to watch what happens afterwards. and you have to stay there and then stay plugged in and stay focused on the destruction that you just caused from your aircraft. narrator: in 2012 alone, the u.s. carried out hundreds of drone strikes across four countries. afghanistan is the only publicly authorized war while strikes in pakistan, somalia and yemen are covert cia operations performed without putting american lives on the line. singer: the technology has enabled us to set aside some of the risk factors of sending a pilot in harm's way. so, it's meant that we've conducted a lot more strikes that would have been more problematic if we were using manned systems. narrator: the u.s. claims drones have decimated al qaeda's top leadership while causing limited civilian casualties, but the facts are hard to come by. shuja nawaz: we know fairly well how many strikes are occurring. what we don't know is the details-- who the targets were whether they were actually eliminated, or whether some other people were killed-- because verification is very difficult. narrator: there are no fully reliable counts of civilian deaths, but some critics claim that as many as 30% of those killed in the broader drone wars are civilians and that the strikes turn people against the u.s. and violate international law. after more than ten years of attacks, the u.s. officially acknowledged its use of drones to target al qaeda members in april 2012 when presidential advisor john brennan gave a speech. the united states government conducts targeted strikes against specific al qaeda terrorists sometimes using remotely piloted aircraft, often referred to publicly as drones. narrator: he was met with a strong reaction. ...hundreds of innocent people we are killing with our drone strikes in pakistan and in yemen and somalia. they deserve an apology from you, mr. brennan. i speak out on behalf of the constitution, on behalf of the rule law. i love the rule of law. i love my country. you're making us less safe by killing so many innocent people around the world. shame on you! benjamin: thank you. nawaz: it's very critical that the u.s. public understand what is happening with the use of this technology because it is being done in the name of the united states. narrator: drone technology enables america to strike virtually anyone anywhere, with ease, regardless of national boundaries. singer: we've seen the deep controversy that surrounds these strikes in places like pakistan, or yemen, or somalia and a whole new series of questions for international law. the fact that you are not flying a human being across a national boundary still makes it an invasion of a country. we've entered an era where we're conducting an array of operations using unmanned systems that in a previous generation we would have called war and we would have treated like war. when you're conducting more than 300 air strikes into a country you're conducting the equivalent of at least an "air war" campaign. but we don't call it that now. narrator: drones can strike with pinpoint precision, but their visual sensors are limited in ways that can lead pilots to make mistakes. chad: as they stand now, the limitations they have with the predator is not being able for the pilot to look around and see what's going on. narrator: when the operator zooms in to see detail, it's like looking through a soda straw and the pilot loses the broader picture.

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