



A few miles out of Washington, on Route 1 to Baltimore, lies an inconspicuous military installation called Fort Meade.

You would not notice it unless you knew what to look for. In fact, on most road maps, Fort Meade does not exist.

And yet it contains the largest mass of secrets in the world.

It is home to the National Security Agency (NSA), the least visible but most powerful spy agency in America's armoury.



38,000 people work at the agency every day, more than the CIA and FBI put together - every one of them sworn to a lifetime of secrecy



In the enormous post-mortem exercise over what went wrong in the run-up to 11 September, all the criticism has been directed at the Central Intelligence Agency and the Federal Bureau of Investigation, which is how the US Government wants it.

The less attention the NSA gets the better - the joke is that its initials stand for No Such Agency - and yet somewhere hidden in its massive computers there are almost certainly enough vital clues to have prevented the 11 September attacks, had anyone known where to look.

Listening in

The NSA's job is to eavesdrop on the world's phone calls and emails, but do not try to phone them.

The NSA website does not list a phone number. You do not contact them. They listen to you.

You are not allowed to take any pictures of the base. Your only option is to order a video which they shot themselves.

Having finally found a phone number, I rang to ask for it and offered to send a courier to pick it up.

The lady on the end of the phone who called herself a press officer - what a curious job that must be since no NSA official has ever given an interview - said that it would not be possible to pick it up because the courier would not be allowed near the camp.

Instead they send it to you.

I even tracked down the Phoenix Society, the association for former NSA employees. I phoned the number listed but an answer-phone simply clicked on without a message.

It is as if an entire city has got a highly contagious disease and is sealed off from the outside world.

Secret world

Though invisible on the map, 38,000 people work at the agency every day, more than the CIA and FBI put together - every one of them sworn to a lifetime of secrecy.

They have their own police force, shopping malls and sports complexes - and their own television network, complete with newsreaders.

On one channel you can watch live video from unmanned planes flying over Afghanistan or surf through real-time satellite photos of Pakistan troop movements on the Kashmir border.



One of the most bizarre ironies of all this is that five of the hijackers lived in a motel right outside the gates of the NSA



On their secure internet, which they share with the CIA and FBI, you can read transcripts of intercepted conversations between soldiers on exercise in China, or European diplomats.

When Osama bin Laden first moved to Afghanistan, the NSA listened in to every phone call he made on his satellite phone.

Over the course of two years it is believed they logged more than 2,000 minutes of conversation.

Who knows what gems of information the NSA learnt from that which have not been made public.

It all ended when President Clinton ordered the cruise missile strike on his training camp in 1998. Bin Laden narrowly escaped with his life.

He realised that the NSA was listening in and ditched his satellite phone, and ordered his aides never to talk on the phone again about operations.

Terrorist neighbours

This shows the limitations of the NSA's incredible technology.

In my experience, journalists cannot resist endowing spy agencies with supernatural capabilities and power. In fact their failings are all too human.

September 11 is a perfect example of this.

Nineteen men armed only with box-cutters and their fanaticism successfully hatched a plot totally unnoticed by America's $40bn a year intelligence-gathering machine.

They succeeded because they lived and worked, not in the shadows where spies operate, but in full view.

In fact, one of the most bizarre ironies of all this is that five of the hijackers lived in a motel right outside the gates of the NSA.

Early on the morning of 11 September, when Hani Hanjour and his four accomplices left the Valencia Motel on US route 1 on their way to Washington's Dulles airport, they joined the stream of NSA employees heading to work.

Three hours later, they had turned flight 77 around and slammed it into the Pentagon.

The NSA was created after World War II to stop another surprise attack like Pearl Harbor by providing early warning.

But in the hour when the need was greatest, it failed the country. And it failed not because it did not have enough information, but because it had too much.

According to author James Bamford, who has studied the NSA for years, each one of their dozen largest listening posts around the world picks up more than two million communications an hour - cell phones, diplomatic traffic, emails, faxes.

That works out at 500 million hours every day.

When you think that this has to be translated from a myriad of languages and then analysed, you realise that the NSA looks less like an omniscient being than a man wading through a warehouse of words in search of a few tiny diamonds.