The launch was then delayed by about an hour due to a ground system helium issue.
Watch the launch live here.
If you see a rocket in the sky tonight, don't panic it's supposed to be there.
The office is in charge of designing, building, launching and maintaining US intelligence satellites.
The launch will be the agency's first in 2018 at the air base northwest of Santa Barbara. The Delta IV M+(5,2) and Delta IV M+(5,4) have two and four SRMs, respectively, and 5-m-diameter PLF.
Colonel Greg Wood, 30th Space Wing vice commander, said: "We are ready and eager to take on this Delta launch". These have been used on the Delta IV since its initial flight in 2002.
Additionally, Orbital ATK manufactured the propellant tank for the Delta IV upper stage roll control system at the company's Commerce, California, facility, and designed and manufactured the nozzle for the Delta IV's RS-68A engine at its Promontory, Utah, facility.
"The successful launch of a payload in support of our national security and that of allied forces demands the best propulsion systems available", said Aerojet Rocketdyne CEO and President Eileen Drake in a statement issued by the company. While it's no longer a secret, it does still use its systems to collect information and "Play a crucial role in providing global communications, precision navigation, early warning of missile launches and potential military aggression, signals intelligence, and near real-time imagery to USA forces to support the war on terrorism and other continuing operations", according to the NRO site.