It looks like something out of a spy film and has a wingspan longer than a football pitch.
The world's largest plane has been unveiled by Microsoft co-founder Paul Allen after it left its hangar in the California desert for the first time.
The "Stratolaunch" has a wingspan of 385 feet, weighs up to 580 tons and has six jet engines. But it isn't meant to carry passengers.
The plane is designed to launch rockets into space from the air, saving jet fuel compared to the process of launching them from the ground and vastly reducing the cost of sending cargo into space.
It was moved out of its hangar for "aircraft fuelling tests", according to Stratolaunch Systems, putting the end to its construction and paving the way for ground flights. It expects to demonstrate its first launch as early as 2019.
It stands 50 feet high, has 28 wheels and is expected to have a range of 2,000 nautical miles, flying at the altitude of around 35,000 feet, roughly the same as commercial planes.
The wingspan makes it the largest plane in the world, finally surpassing Howard Hughes' "Spruce Goose", the enormous wooden plane built by the famous entrepreneur that made its first flight in 1947.
Allen, who was obsessed with rockets as a child, co-founded Microsoft with Bill Gates in 1975.
He left the company in 1982 because of health reasons but retained a sizeable stake in the company.
According to Bloomberg he has a net worth of $21.4bn (£16.6bn), making him the 35th richest person in the world.
He wrote last year: "Opening up access to LEO (low earth orbit) will deliver many benefits. For example, we could deploy more satellites that would enable better understanding of why our weather patterns are changing and help increase agricultural productivity.
"And, we could study atmospheric chemistry more closely to better study and mitigate climate change.
"But none of this will happen as quickly without exploring new, flexible and streamlined ways to send satellites into orbit."
The Stratolaunch project was first announced in 2011. It is designed to be able to launch multiple rockets, and doing so from a moving aircraft can evade the weather problems that afflict many rocket launches.
It isn't the only company to attempt to launch rockets from planes. Sir Richard Branson's Virgin Orbit announced plans to do so from a Boeing 747-400 jet in 2015.
Other tech entrepreneurs including Elon Musk's SpaceX and Jeff Bezos' Blue Origin are also seeking to reduce the cost of space travel.