Before the Laundry, things were a bit confused. You can do magic by hand, without computers, but magic performed by ritual without finite state automata in the loop—calculating machines, in other words—tends to be haphazard, unreliable, uncontrollable, prone to undesirable side effects, and difficult to repeat. It also tends to fuck with causality, the logical sequence of events, in a most alarming way.

We've unintentionally rewritten our history over the centuries, would-be sorcerers unwinding chaos and pinning down events with the dead hand of consistency—always tending towards a more stable ground state because chaos is unstable; entropy is magic's great enemy. When the ancients wrote of gods and demons, they might well have been recording their real-life experiences—or they may have drunk too much mushroom tea: we have no way of knowing.

Let's just say that you can't always trust the historical record and move swiftly on.

On the other hand, unreliability never stopped anyone from using a given technology—just look at Microsoft if you don't believe me.

During the nineteenth and early twentieth centuries, the scholars of night systematized and studied the occult with all the zeal Victorian taxonomists could bring to bear. There was a lot of rubbish written; Helena Blavatsky, bless her little cotton socks, muddied the waters in an immensely useful way, as did Annie Besant, and Krishnamurti, and a host of others.

And then there were those who came too damned close to the truth: if H. P. Lovecraft hadn't died of intestinal cancer in 1937 something would have had to have been done about him, if you'll pardon my subjunctive. (And it would have been messy, very messy—if old HPL was around today he'd be the kind of blogging and email junkie who's in everybody's RSS feed like some kind of giant mutant gossip squid.)

Then there were those who were sitting on top of the truth, if they'd had but the wits to see it—Dennis Wheatley, for example, worked down the hall in Deception Planning at SOE and regularly did lunch with a couple of staff officers who worked with Alan Turing—the man himself, not the anonymous code-named genius currently doing whatever it is they do in the secure wing at the Funny Farm. Luckily Wheatley wouldn't have known a real paranormal excursion if it bit him on the arse. (In fact, looking back to the dusty manila files, I'm not entirely sure that Dennis Wheatley's publisher wasn't on the Deception Planning payroll after the war, if you follow my drift.)

But I digress.

It was to our great advantage during the cold war that the commies were always terrible at dealing with the supernatural.