Spending on the planes is expected to total at least $12 billion over the next five years, up from $300 million in 2001, to pay for at least 132 UAVs, including a new version for the navy, updated models for the army and a major effort to solve technical problems.
Unmanned aerial vehicles (UAVs) were heavily used after the February 22 bombing of a mosque in Samarra, Iraq, demonstrating the military's need for vehicles that can drop bombs or hover over targets without risking pilots' lives.
When Iraq erupted in ethnic violence after the attack on the mosque, UAVs were deployed over trouble spots to monitor where crowds were gathering and whether they were armed or violent.
Referring to the growing demand for Predator UAVs in Iraq, Dan Goure, defence analyst at the Lexington Institute, said: "Now the revolution has come. And it's going to be explosive over the next few years."
Crowded in Iraq
At least 700 UAVs of all shapes and sizes are being used in Iraq, with dozens often jostling for room in the crowded airspace 24 hours a day.
The US Army controls about 600 of them, mostly the smaller Ravens that soldiers can carry in backpacks and send up for surveillance.
So far there has been one reported collision of a small UAV and a helicopter in Iraq, according to Major-General Norman Seip, assistant deputy chief of staff for air operations.
He said no one was injured.
The larger unmanned air force Predators flown remotely by airmen sitting at consoles in a Nevada base have been used to bomb strongholds of fighters in Iraq, and the Pentagon plans to buy an extra 219, along with 35 Global Hawks.
UAVs in proposed 2007 US budget
Goure predicted that spending in 2007 could reach $2.5 billion, although some of it will be hidden because it is classified or buried in other programmes.
The government buys many different unmanned systems for the military and the intelligence community also buys its own.
The navy, which has spent comparatively little on unmanned vehicles, is preparing to buy a new helicopter-like UAV called the Fire Scout that can take off and land vertically on ships.
The technology has changed greatly since the first remote-controlled drones were used to train anti-aircraft gunners during the second world war.
During the Vietnam war, the air force used jet-powered drones carrying cameras to spy on North Vietnam and China.
The newer models gained widespread use for the first time in the Kosovo war in 1999.