TOKYO — In July, the Air Force’s newest unmanned plane, the MQ-9 Reaper, flew its first mission over Iraq.

This beefier version of the older Predator had been in Afghanistan for months, logging 3,800 hours, the Air Force said at the time. In addition to bolstering the military’s 24-hour aerial surveillance, the 10 new Reapers each can carry six times the weapons weight as the Predator.

But before the Air Force celebrated the Iraq mission for its newest drone, it issued a notice: It wants a more flexible, weather-hardy unmanned plane in the next seven years.

In May, the Air Force Materiel Command called for submissions for a drone that can better adapt to specific missions and survey a more varied terrain.

The overall goal is to add 50 new combat air patrols, or CAPS, units staffed with three to four planes. With those CAPS, and additional planes for training and testing, it means the Air Force is looking at 270 new unmanned planes in its fleet. Some will be some flying by 2015, according to Lt. Col. Ken Kilmurray, a deputy chief at the Air Combat Command at Langley Air Force Base.

Already this year, the Air Force is looking to add another 31 CAPS of Reapers to its fleet. Currently, the service has about 100 Predators and 10 Reapers.

"We’re in a steep growth curve," he said during a phone interview.

It’s also a steep spending curve.

For projects such as the unmanned vehicles, the military thinks about money in five-year segments. From 2008 to 2013, the military plans to invest $3 billion in research, development and production of the new version of the Predator, according to Kilmurray. From 2010 to 2015, the Air Force wants to add another $35 billion to the proposal, he said.

With the new generation, the Air Force is looking for a drone that can withstand dangerous weather conditions and can fly fully armed higher than 30,000 feet, faster than 250 knots, according to Kilmurray. The military would also like the new design to include a system that allows a pilot to fly more than one plane at a time, he said.

Moreover, the current Predators and Reapers have a similar problem: They are based on 1980s technology and are nearly impossible to refit for specific missions, according to Kilmurray. For example, adding another sensor to look through jungle canopies or search for roadside bombs can take several months to a year, he said.

"That’s a primary weakness," he said. "And there’s technology out there. And it’s better."

The Air Force began overseeing UAVs in 1996. These early drones were eyes-only, a problem that became more apparent as ground-based pilots watched enemy action ensue before reinforcements could arrive, Kilmurray said.

Kilmurray flew Predators in Kosovo, and he remembers watching the enemy’s movements but being unable to respond in real time.

"I couldn’t call other backup in time," he said. "The Predator was only able to watch."

Now, Predators and Reapers are equipped with Hellfire missiles, and the newer Reapers are loaded with more than a ton of weaponry. Both transmit more than just naked-eye video; they also use synthetic aperture radar, which can see through clouds by bouncing multiple signals off a target and combining data to "resolve" the object.

The Air Force isn’t looking to add more munitions to the future drone, Kilmurray said.

What the Air Force wants, he said, is 24-hour coverage of the battlefield. During the past year, the number of combat Predators and Reapers in the air at any time has more than doubled to 27 aircraft worldwide, according to a Pentagon news release.

The Army also uses its versions of unmanned aerial vehicles in Iraq. Some of the smaller, hand-launched aircraft are "slightly better, a more modern version" than the Air Force’s, Kilmurray acknowledged.

The ground forces also have formed their own air surveillance mission, a move some see as the result of frustration with the Air Force’s fleet, The New York Times reported in June. The Air Force said its small fleet put the control of the craft in top-level commanders, sometimes making response less nimble, sometimes delaying response times, the paper reported.

Kilmurray said the Predators and Reapers can support all levels of ground forces, from platoon on up. He also said the services can work together with both systems, but that neither system is made to fly together. The idea is to increase the number of drone eyes on the ground, rather than have two or three planes zeroing in on the same target.

"We want to spread capability as much as possible," he said.

For the Air Force, another goal is to use its drones to replace some work done by the F-16s, Kilmurray said. The fighter jet fleet is not shrinking, Kilmurray said. But Reapers draw less anti-aircraft fire, which allows them to dwell over the target with less threat, he said in an e-mail.

But commanders still need a mix of manned and unmanned planes in the air, he said.

"A Predator does not replace a manned aircraft in all situations," Kilmurray said. Yet it’s not ideal to have a "manned fighter in all phases of war. I need a mix."