Since its debut in 1969, the Boeing 747 has been called upon for its fair share of special missions, from carrying U.S. presidents to fighting forests fires. Here, a look at five of the coolest modifications in the jumbo jet's history.

Air Force One

Perhaps the most famous airplanes in the world, the "Flying Oval Office" is actually a pair of specifically modified, sel-sufficient Boeing 747-200Bs (or VC-25s in Air Force terminology) that use the call sign "Air Force One" when the sitting U.S. president is on board. The planes have 4,000 square feet of interior floor space and such special features as air-to-air refueling, a medical operating room, and other classified perks. The current planes were delivered in 1990, during the presidency of George H.W. Bush, and are expected to be replaced soon with updated 747-8i models.

Boeing 747 Dreamlifter

Boeing created the hulking 747 Dreamlifter cargo plane for a very specific purpose: to haul 787 parts that were too massive for other forms of transportation to its production facilities in Washington state. The modified 747-400 features a bulging midsection that has earned it comparisons to the Oscar Meyer Wienermobile, and, at 65,000 cubic feet, its enormous cargo is the world's largest by volume.

Stratospheric Observatory for Infrared Astronomy (SOFIA)

A modified United 747SP was transformed into SOFIA, a joint project of NASA and the German Aerospace Center (or DLR) designed to carry the world's only flying infrared astronomy laboratory on missions that can take place only at altitudes of about 41,000 feet. The airplane's body features an enormous door that can be opened mid-flight to allow its infrared telescope access to the sky.

Shuttle Carrier Aircraft (SCA)

U.S. presidents aren't the only high-profile cargo carried by the 747. NASA employed a pair of modified 747-100s to transport space shuttles from their landing sites back to Kennedy Space Center, as well as on numerous test flights. The aircraft's range was reduced to a mere 1,000 nautical miles due to the dramatically increased payload of the space shuttle, which is mounted atop the the plane, piggyback-style.

Evergreen 747 Supertanker

The world's largest firefighting plane debuted in 2009 in the shell of a 747-100 and is capable of dropping nearly 20,000 gallons of fire retardant or water on large fires. An updated version, flying under the name Global Supertanker and built on a 747-400 frame, was used for the first time in the U.S. this summer to fight a Northern California wildfire.