For four years, a doctor commuted between his clinics in Texas in a $5 million turboprop with jazzy metallic stripes and ruby stones embedded on the drink cabinet. The jet featured exotic wood veneers and polished chrome, and his daughter?s initials were in the tail number.

But after a mysterious buyer snapped up the plane in 2008, it ripped out the fancy appointments, painted it a dull grey and sent it on a more dangerous mission. Unknown to the doctor, his prised King Air 350 had become a spy plane, one of the first of a new military model that is now easing the load on the unmanned drones for the United States in Iraq and Afghanistan.

For a military that loves to create shiny hardware from scratch, dipping into the used-plane market is a rarity, done only under the most urgent conditions. Remotely piloted drones have been the intelligence stars of the wars, but the Pentagon cannot build them quickly enough to meet the demand. So, the Air Force bought eight used King Airs and equipped them with video cameras and eavesdropping gear as part of a broader effort to supplement the drones with manned aircraft. The Army has also retooled similar planes to track insurgents who plant bombs.

In turning to the King Airs, the Pentagon has appropriated an aircraft that is commonly associated with business executives flying to meetings and wealthy vacationers to weekend ski outings. King Airs have also drawn celebrity pilots like the late actor and comedian Danny Kaye.

The military has used older King Airs to carry VIPs and conduct other operations in the past. Now, military commanders say the twin-propeller planes, which carry two pilots and two sensor operators, have carved out a niche in working more closely than the unmanned drones with soldiers on hazardous missions. The crews on the planes, now called MC-12s, are in nearly constant radio contact with convoys and troops in firefights. They can chat more easily with them than the drone crews, which are based in the United States, to position the spy gear and interpret data about enemy movements.

With budget cuts looming, Air Force officials say the rapid fielding of the MC-12s also shows how the military could make greater use of commercial products to reduce costs and contracting delays. In addition to the used planes, the Air Force has fielded 29 new King Airs with the surveillance gear, and the Army would like to buy 36.

?For me, this is a precursor of what we?re trying to do across the board,? said David M Van Buren, a top Air Force acquisition official, though that could be easier said than done with more complex weapons. Van Buren said the Air Force turned to the used planes after Robert M Gates, then the defence secretary, ordered to rush more spy planes into the air.

Each of the used planes ? some had been owned by law firms and companies ? were outfitted differently. One had a stereo and high-definition television system. The manufacturer, Hawker Beechcraft, had picked the ruby theme for the doctor?s to celebrate the model?s 40th anniversary in 2004. And perhaps in a foreshadowing that the plane would eventually be put to a broader use, the words ?Free Enterprise,? a motto of one of Beechcraft?s founders, were emblazoned under the cockpit window.

An Air Force contractor, L-3 Communications, found the eight used planes with the least wear and tear. It then ripped out the plush interiors. Bubinga wood veneers gave way to computer stations for the surveillance specialists and miles of wiring for three communications networks at different secrecy levels. A camera ball was hung from the belly, and 16 antennas were added.

Meanwhile, the Air Force gave a no-bid contract to Hawker Beechcraft to build 29 extended-range planes at $7.5 million apiece, the average discounted price for commercial customers. An L-3 plant in Texas then worked around the clock to install the spy gear, which cost $13 million a plane.

At least eight corporate plane buyers let the military slip ahead of them in the production schedule. Several more slots opened as the recession forced others to cancel orders. Terry Harrell, a Hawker vice president, said Hawker had risked $35 million to $40 million of its own money to start building the planes before the contract was signed.