This story was updated at 2:40 p.m. EST with details of the flight.

Stratolaunch, the private launch company founded by the late billionaire Paul Allen, has just flown the world's largest aircraft for the first time.

The massive airplane, which has a wingspan bigger than a football field and is designed to launch rockets from the air, took off on its maiden test flight from the Mojave Air and Space Port in Mojave, California, this morning (April 13).

"We all know Paul would have been proud to witness today’s historic achievement,” his sister Jody Allen, chair of Vulcan Inc. and trustee of the Paul G. Allen Trust, said in a statement released by Stratolaunch today. "The aircraft is a remarkable engineering achievement, and we congratulate everyone involved.”

The flight, while not officially announced beforehand by Stratolaunch, was spotted by photographers at the airport, where the company has been conducting runway tests with the giant plane in recent months.

"It was surprising. In a way, I expected it to take longer," aerospace photographer Jack Beyer told Space.com after watching the plane's takeoff, adding that it almost felt anticlimactic. "And then I realized it was actually effortlessly in the air and was astounded." Beyer is posting his views of the Stratolaunch test on his Twitter and Instagram.

RELATED: Stratolaunch Test Photos: The World's Largest Plane in Action

Image 1 of 3 Stratolaunch's rocket carrier plane, the largest aircraft ever built, takes off from the Mojave Air and Space Port in Mojave, California during its first test flight on April 13, 2019. (Image credit: Stratolaunch) Image 2 of 3 Stratolaunch's huge satellite-launching plane Roc soars over California's Mojave Desert during its first-ever test flight on April 13, 2019. (Image credit: Stratolaunch) Image 3 of 3 Crowds cheer the first-ever liftoff of Stratolaunch's huge carrier plane Roc on April 13, 2019. (Image credit: Stratolaunch)

WOW. First flight of the worlds largest airplane. History is made. @Stratolaunch @NASASpaceflight #stratolaunch pic.twitter.com/e7x0omxvVcApril 13, 2019

The huge airplane, named Roc, took off at 6:58 a.m. PDT (9:58 a.m. EDT; 1358 GMT) and stayed aloft for 2.5 hours, Stratolaunch representatives said in the statement. Roc reached a peak altitude of 17,000 feet (5,180 m) and a top speed of 189 mph (304 km/h), they added.

The flight, which allowed pilots to evaluate Roc's performance and handling, ended with a touchdown back at Mojave Air and Space Port.

Crowds cheer the first-ever liftoff of Stratolaunch's huge carrier plane Roc on April 13, 2019. (Image credit: Stratolaunch)

Founded by Allen in 2011 , Stratolaunch is a private spaceflight company that seeks to launch rockets into orbit from high altitude using its novel megaplane carrier aircraft. The plane was built for Stratolaunch by Scaled Composites, the Mojave-based aerospace company that also built SpaceShipOne, the first commercial suborbital spacecraft.

The carrier plane is enormous, the largest ever built. It features twin fuselages and six jet engines, and has a wingspan of 385 feet (117 meters) — long enough to cross an American football field from end zone to end zone. That's about the same length as the International Space Station.

Stratolaunch: Biggest Aircraft in History to Launch Spaceships (Infographic)

The aircraft is designed to fly satellite-carrying rockets to an altitude of about 35,000 feet (10,700 m), then release the boosters so that they can launch their payloads up to orbit.

"A historic milestone for the Stratolaunch team with this record setting aircraft taking flight," Thomas Zurbuchen, NASA's associate administrator for NASA's science directorate, wrote on Twitter . "This is about going to the edge of space and beyond!"

The world’s largest airplane takes flight! @Stratolaunch @NASASpaceflight #stratolaunch pic.twitter.com/jmLs3mpztnApril 13, 2019

Stratolaunch initially teamed up with the spaceflight company SpaceX, which was going to build a modified version of the Falcon 9 rocket to launch from the giant carrier plane. But the two companies split within a year. Orbital Sciences (later Orbital ATK and now Northrop Grumman) then stepped in, with a planned new rocket called Thunderbolt.

But in 2016, Stratolaunch announced plans to use smaller rockets (Orbital ATK's Pegasus XL vehicles). At one point, Stratolaunch was also developing its own series of rockets and spacecraft, including a small space shuttle, to launch from the massive carrier plane. But earlier this year, the company shut down that program to focus on launching smaller Pegasus XL rockets built by what is now Northrop Grumman.

"What a fantastic first flight," Stratolaunch CEO Jean Floyd said in the same statement. "Today’s flight furthers our mission to provide a flexible alternative to ground-launched systems. We are incredibly proud of the Stratolaunch team, today's flight crew, our partners at Northrup Grumman’s Scaled Composites and the Mojave Air and Space Port."

Here are some more views of Stratolaunch's historic first test flight.

Roc spreads her wings and the worlds largest airplane tastes the air for the first time! #Stratolaunch @NASASpaceflight pic.twitter.com/albte00VbgApril 13, 2019

According to Beyer, a large crowd of spectators watched Stratolaunch's test flight. It wasn't a massive crowd, but a larger gathering than he saw during recent suborbital space launches from the Mojave Air and Space Port by another private spaceflight company, Virgin Galactic.

At Mojave Air and Spaceport this morning once again hoping to catch the first flight of the world’s largest plane. Roc, as the aircraft is known, is now sitting at the end of runway 30 poised to make aviation history. @Stratolaunch @NASASpaceflight pic.twitter.com/ViFMoJfs8bApril 13, 2019

The wild blue yonder just got a little more wild! #Stratolaunch @NASASpaceflight pic.twitter.com/hC2I5WZjFSApril 13, 2019

So #Stratolaunch is end of runway....this could happen... pic.twitter.com/aWrUrOWo55April 13, 2019