Bear in mind that Gerry Anderson's mind's universe was a lot more advanced than ours. The first Eagle transporter was supposed to have landed on the Moon back in 1972, followed by the establishment of various moonbases. Not just Alpha, but the secret Moonbase run by SHADO.
During a crisis starting in 1980, where some extraterrestrials tried a clandestine invasion of Earth, SHADO is said to have developed plans for a more fighterly version of the armed Eagles, capable of delivering a lot more punch than SHADO's three little one - nuke Interceptors. The Mark IX Hawk was the brainchild - but after the UFOs kind of stopped, the only three Hawks built were kept in mothballs in the Centuri station at the Lagrange point between the Earth and the Moon, and were destroyed when the Moon blasted free of the Earth's orbit.
In the TV show, the Mark IX Hawk only made one appearance in the entire show - season 1, episode 4, War Games, where they were sent from a planet of psions as a manifestation of the Alphans' deepest fears. The Hawks wiped the Eagles out of the sky.
Don't mess with melon-headed psions.
Also, the Seventies were wild.