It was pure serendipity, according to Treyarch. Forget how the studio is essentially delivering at the start of a wave of stereoscopic titles, and neatly beating Sony's mega-hyped 3D support for Killzone 3 to release with its own all-conquering franchise; it was all just a lucky coincidence from some of Treyarch's R&D developers who decided to play around with 3D rendering. Only, they say, it looked good. Really good. Better than any other 3D shooter in development, they say. So it's now in the game.

For all the considerable amounts of flak Treyarch gets, it's refreshing to see a studio unafraid to muck about with ideas and include their unlikely favourites in final code. World at War's Zombies went from a source of ridicule to a much-loved favourite overnight, and Black Ops' promising newbie-friendly Combat Training was initially developed as a tool to test weapon balancing. 3D isn't going to upset the franchise's tone in the same fashion as turning Nazis into the walking dead, but it's another feature born out of Treyarch's same desire to tinker and modify.

So, here are the technical details: the game is stereoscopic 3D out of the box for 360 and PS3, with the PC version running on NVIDIA 3D. You'll need the required assortment of a 3D television, fancy glasses and bottomless pockets, but if you've somehow got that all in place then you can easily flick to stereoscopic 3D from the game's options screen.

The 3D trickery comes with all the similar trappings of other 3D technology - a slightly odd feeling in your eyes as you accustom yourself to the screen, for instance. But once you're all settled then it's easy to stare at the display for a protracted period of time without any discomfort; that's key to the implementation, too, seeing as people (and by people, I especially mean me) tend to binge on multiplayer for hours on end.

To support the technical demands of rendering fancy 3D, the game [on consoles] runs at a slightly lower resolution than the 2D implementation. I also observed a noticeable drop in frame rate from Call of Duty's trademark silky smooth 60, though Treyarch assured me the game had been 'optimised' to run in 3D.

The effect works better in certain areas than others, of course. Treyarch showed the opening of the game's third mission, Numbers, which starts with you interrogating a soon-to-be informant in Kowloon City. The money shot is right there at the opening, as you bang the poor guy's head into a window pane. Only you'll look straight past that, instead focusing on the world outside the window; the depth of field is particularly striking here, and the 3D effect looks incredible. I think it's the first time I've ever felt like I'm properly looking out of a virtual window.

The scene quickly moves on to your character breaking said window, picking up a shard of glass and depositing it into the man's mouth before punching him in the face a few times. The victim is left spitting out bits of bloodied glass. For the record, it still looks pretty grim without the 3D glasses.

It all goes - surprise surprise - a bit tits up after that, so before long you're getting stuck into densely packed corridors of enemies and dodging bullets over the rooftops of Hong Kong. It's all greys, neon and angles, with you scrambling for (ideally) a shotgun to take out the swarm of enemies congregating on your position.

One of the biggest problems, though, is on-screen text. This is fixed to the front plane of display, but it's a 2D image stuck in a 3D world. It's workable, but it doesn't look quite right - though it's more of a restriction of the technology rather than any mistake on Treyarch's part, I think.

But it also affects the 2D crosshairs. These have been turned off by default, and you can see why: it looks really weird with them on. This is especially jarring with the wider crosshair spreads of weapons like the shotgun.

And, of course, Treyarch is also encouraging 3D gamers to use the iron sights as much as possible. Here the game separates the weapon to the front of the screen and the action to the back, and while the effect takes a bit of getting used to it does make you feel like you're actually looking down your weapon.

Some bits will naturally be more striking than others. Rappelling down the side of a mountain in the level WMD looks phenomenal, and when a dense patrol of enemy soldiers walk past you at the start of the same level you get a far more accomplished (and impressive) sense of depth than you would without the glasses.

You'll also come across a fair few sections that don't really pop out at the player, though, and it's with these bits the game's 3D sometimes feels like it's relying on using the iron sights for immediate 'wow' factor. Black Ops hasn't been designed to be viewed solely through 3D glasses, after all, but this is clearly a conceit prospective 3D gamers are going to have to make for a few years to come. When it does work, however, the effect is powerful and striking - good enough to make me Google how much 3DTVs are currently going for. Sigh, if only I was a millionaire.

3D won't appeal to everyone, of course, but what's clear from seeing a few levels in motion is how Treyarch has managed to seamlessly incorporate 3D into Black Ops on the sly. It looks more impressive than what I've seen of Guerrilla's implementation of the same technology in Killzone 3, and it's also very impressive to see it running on the 360. How Treyarch has managed to keep quiet about the fact it's going to be the first blockbuster shooter to support stereoscopic 3D is beyond me, but that's exactly what it's done.

Call of Duty: Black Ops is due for release on Xbox 360, PS3, PC, Wii and DS on November 9.