The bunker's 20m (400ft) Access Tunnel.
It was known as "the hole".
While there is little to see above ground, a long sloping corridor leads deep underground into a secret nuclear bunker.
For more than 20 years, RAF Holmpton was part of a Cold War defensive radar programme called 'Rotor'.
It involved 70 radar stations dotted around the coast.
Built in 1953, the bunker faces east and was able to see hundreds of miles to the Soviet Union, monitoring the superpower as it stockpiled nuclear weapons.
The men and women that worked at the station were responsible for warning of an approaching attack, recording its direction and velocity, and ultimately calculating the fallout of a bomb.
In the event of a catastrophic nuclear war, it would be their job to restore order in the region.
Former Air Defence Operator Barbara Turner said they were known locally as the "moles":
"All the locals that lived around about all knew what was going on... They used to say, 'oh there they go, the Moles.'"
Her sister, Janet Huitt, also worked in the bunker: "They used to know we all disappeared underground by the busload."
It was the job of Air Defence Operators to interpret raw data from radar screens.
They then had to write the results backwards on a clear Perspex "tote" board, so they could be read from the other side.
This information was then plotted on a radar board that Officers seated above could easily monitor.
Air Defence Operator Kath Shimwell said that writing backwards became second nature: "It was not difficult once you got into it, it was just that you had to do it so quick!"
Ted Pattrick was an Observer Officer for Nuclear Reporting Cell 05. He said:
"You couldn't divulge where you were going or what you were doing ... Even my wife didn't know exactly what I did."
"We knew very well we didn't stand a chance if there was a nuclear fallout upstairs because we wouldn't get out", said Janet Huitt.
"There were dry rations hidden in the walls and plenty of water tanks down here.
"So if we ever had to stay down for any length of time we could live for so long on the dry rations but we knew they wouldn't last forever.
"I considered it frontline work, I considered it very important for the security of our country."
Despite the importance of their work, the women of "the hole" earned just a third of the salary of their male counterparts, and received no pension.
They will also feature in 'Hidden: Cold War Women', an exhibition by photographer Lee Karen Stow which will open early next year.