Call of Duty XP: Live dispatch from our embedded reporter

Howard Hughes built the first hangar entirely out of wood in 1943, convinced that structures made of metal were intrinsically unhygenic. In the cavernous interior next door, rumour has it, last week they were filming Batman. Today, right now, Infinity Ward Creative Strategist Robert Bowling is in the central hall and playing to a home crowd.

Walking from one end of the hangar would take at least five minutes – it's a vast space the size and shape of a landing strip you'd usually expect deep inside the Battlestar Galactica. Today, however, you're not walking anywhere. The hall is packed with bodies – some with fists raised, others with unfurled hands alternately moving between forehead and open mouth.

“No One Man Army! No game-ending nuke!” iterates Bowling on-stage wearing his trademark cargo shorts as cheers reverberate around the building. “No shotguns as secondaries!” he underlines to a white noise of whooping. Then, after a fraction of a pause, he says “Definitely no Commando perk!” The room pretty much explodes. Somewhere in maniac heaven Howard Hughes worries about the bacteria simultaneously released by so many sweaty, excited bodies in such close proximity…

Call of Duty XP is a fascinating creation. It's a fan convention, a COD celebration and a marketing feat all in one – and it shines a light on a community as vast and cavernous as the building that currently holds them. Later on as you tread the hangar-floor you have to wind your way past countless fleshy bodies standing stock-still on the temporary carpet staring at screens overhead as if they're decoding the Matrix. Meanwhile commentators with their caps on backwards stalk between 360 pods excitedly yelping the progress of teams as they compete for a million dollar prize-pot – there are dramatic comebacks and there are dismal defeats. I struggle to follow the games, but it's clear that heroes will be made today. And that most competitors will go home wondering just what could have been.

A steady stream of gamers, once they've had their fill of watching the Juggernaut Sumo or showed off their Black Ops capabilities, exit through the gift shop and out into the Californian sun. It's quite fun to stand by the US Army Veterans van and watch them emerge – everyone has at least two seconds where they unconsciously perfectly recreate the motions of Christopher Lee in a climactic Dracula scene.

Out here it's dusty and, fittingly for Call of Duty, a disused air field. If you're a child of the British early nineties you'll understand when I say that the scene looks like what Challenge Anneka would come up with if asked to build a violent Disneyland in forty eight hours. It's arid and at first glance is oddly threadbare, but look past the masses queuing for a pricey slab of meat from the lovingly-recreated Burgertown and there's some quite phenomenal fan material here.

Overhead a zip-wire carries the occasional screaming man down to earth, while his long-suffering girlfriend takes a photo from the most dramatic angle she can find. Behind her, and behind walls of nets, is a perfect recreation of MW2's Scrapyard level where teams of punters spray each other with paintballs while the familiar soundbites of COD battle blare out over loudspeakers.

It was here that, yesterday, that several proud journalists strutted out into battle – only to be unexpectedly faced by an opposing team entirely comprised of US Marines. The predictable Kill/Death ratio told only half the story – throughout this one-sided bout the only direct hits made by the US military were either direct to the head or to the neck. It was the sort of day that made you glad you're not an Afghan goat-herder.

For every activity an XP punter takes part in, as is the way of COD, he is rewarded – this time with a patch that either their mother, some helpful people in the gift shop or the aforementioned long-suffering girlfriend can attach to camo-gear, flak-jacket or pyjamas. It's this badge of honour that the people queuing for three hours for a paintball mosh in the recreated MW2 training pit are after – though sadly there are no actors pretending to be NPCs playing basketball outside, or shooting the shit with you upon entry.

Call of Duty XP is genuinely remarkable – a window into the soul of a franchise that's frequently accused of being constructed without one. It's strange to stand amongst it all and realise that here there is no cynicism, no Acti-hate or torrid internet opinion. There's just a shared love of this monolithic gaming franchise, and for the outsider it feels as refreshing as for the attendees it is life-affirming.

I share a cab-ride back to the hotel with a wheezy man from Detroit. We discuss quick-scoping and noob-tubing for a while, or at least he does his best to discuss them at me. I ask him what his plans are for the evening. “I'm just gonna go up to my room.” he explains. “Gonna play some Black Ops…” It's at this point I realise that I've seen everything.