It's been 75 years-that's three-quarters of a century-since the prototype of the Flying Fortress series took to the skies for the first time over Seattle, Washington.

For so many reasons, the B-17 Flying Fortress became an American icon.

That 75th milestone was reached this week-Wednesday-with three B-17s in attendance at AirVenture 2010. From the Gulf Coast Wing of the Commemorative Air Force (CAF), a long-time air show B-17, "Texas Raiders," shares space on AeroShell Square with other crown jewels of aviation.

Texas Raiders has spent the past 47 years in the care of the CAF. Its evolution is emblematic of the civilian Fortresses.

When first purchased by the CAF in 1967, the bomber kept civilian paint and markings, gradually transitioning to military paint schemes of varying authenticity. No turrets were fitted for a number of years, but by the early 1980s expectations on the appearance of warbirds coincided with the acquisition and installation of a lower ball turret and the distinctive chin turret.

The CAF made a deliberate decision-as have some other warbird restorers-to keep its complete Sperry top turret in the hangar instead of in the bomber, since the floor-to-ceiling presence of the Sperry would inhibit tours from nose to tail. So Raiders flies with a realistic Sperry turret dome, but a clearer passageway inside.

Maintaining and campaigning a veteran like Texas Raiders makes for some other challenges-ones with dollar signs as the price and scarcity of B-17s and parts just go up.

In fact, Texas Raiders is back on the circuit this year after more than seven years of rebuilding at Houston's Hobby Airport, a project launched after inspections revealed substantial corrosion that demanded disassembly of much of the structure and machining of fittings.

With a ruggedly authentic paint scheme and dummy guns bristling, "this is as close to original as we can get," says her flight engineer, Rick Thomas.

That mandatory rehabilitation cost nearly $600,000-bucks not easily raised. That is the degree to which the stewards of the remaining B-17s must go to ensure their safe preservation.

Also hailing from the Gulf Coast, the B-17G Thunderbird represents a combat veteran of the same name. Owned and cared for by the Lonestar Flight Museum in Galveston, Texas, Thunderbird somehow avoided the issues faced by Texas Raiders, but Lonestar's facilities were ravaged by Hurricane Ike in 2007.

Thunderbird flew to safety, but the savagery of the saltwater storm surge damaged many valuable spare parts.

Money, always tight at warbird museums, got tighter as repairs from Ike drained the coffers. Pilot Doug Peoples says Lonestar would like to replace the nonstandard Plexiglas nose with a new-made standard bubble, but for the moment the multi-thousand dollar cost is out of reach.

Economic times have changed Lonestar's flying schedule for Thunderbird, Peoples notes. "We used to do 20 shows a year," recalls. Now, five or six road trips and some local hops constitute a season for the B-17, beset with a scarcity of sponsors to foot the bill.

The third Fort at AirVenture is EAA's own B-17G Aluminum Overcast, operating out of Appleton this week to provide rides.

Visible overhead throughout the week, the EAA's flagship Fortress is the survivor of its own major rebuilding. And earlier this year, its lower ball turret, a constant source of fascination for visitors, was refurbished to operating condition.

There's a common thread running through all three of these Forts at AirVenture.

Though youngsters in Flying Fortress years (they are 65 years old), these rare bombers all survive only because of the tireless attention of their crews, and donations from thousands of air show visitors who appreciate seeing these icons of American flight in their element.