The concept of distributing a game for no cost, once the domain of Facebook app-clones and mobile platforms, has quickly become commonplace in PC gaming. We've all seen clear evidence of such a phenomena, from the lessened emphasis on subscription models in MMOs to the availability of quality multiplayer shooters like Tribes: Ascend from a single download. In a blog post, Positech Games head and Gratuitous Tank Battles creator Chris Harris says the psychology of free gaming boils down to letting players set their own sense of worth before asking for money.

"Free to play works because it doesn’t ask you to value the game until you already feel you own it," he writes. "How much would you pay for Farmville to buy it outright? Maybe $5? But play the game for free for a month, build up your farm, invest it, and then hit a plateau in the game where you really need to buy coins to continue, and suddenly your game is worth a lot more than $5. You value the game you already own very highly, and so buying add-ons for it is just common sense. I suspect this is why DLC works so well and sells so well. You have already made a commitment to valuing the game by investing your time. Only a fool could try to rationalize not spending money on it now."

It's almost as if Harris stumbled upon the secret formula of free-to-play games: foster a sense of ownership to encourage microtransactions and DLC. Item-heavy games such as Team Fortress 2 and PlanetSide 2 let you try out a shiny weapon for a short period before taking it away, but that brief usage could boost the likelihood of a wallet getting pulled out simply because you determined your own measure of worth on the item you fleetingly "owned."

Let's hear your comments. Do you only drop dollars on free-to-play games after you've built up a sense of attachment to them, or are your buying habits more free-form?

Positech's inspired tower defence/strategy game Gratuitous Tank Battles has just been given an expansion, which returns the tank-obsessed title to its World-Warring roots. The DLC, available for a modest £4.84, adds new American and German WWII units, plus a new single-player campaign comprising eight maps.

For the unfamiliar, Gratuitous Tank Battles takes place in an alternate future where World War I never ended. We were quite big on tanks back then, and that's continued to the year 2114. The Western Front moves the action back to 1944, which means lasers are out - at least for some of the missions - and old, authentic military equipment is in. Positech's Cliff Harris elaborates:

"Half the battles are set before the introduction of newer weapons such as mechs and lasers and are fought purely with the weapons of the time. The final 4 battles add modern weapons to the mix. Surely you have always wanted to fight against tiger tanks armed with laser guns?" Yes - yes we have Cliff, but it's rude to spy on our dreams.

The Western Front is available to buy direct from Positech, while other portals such as Steam will get it soon. If you want to spy before you buy, there's a DLC trailer below.

Gratuitous Tank Battles is the result of experimentation with the tower defence genre, yielding a strategy game where you attack as much as entrench. Experimentation with units means players can make their own machines and turn them on their foes. And experimentation with AI means the computer can use your creations against you in an endless arms race of tanks, mechs and laser-toting Tommies.

Fittingly for a world where the Great War never ended, very few units will make it through: hundreds will die in a pointless bloodbath to gain just a few inches of ground. But GTB’s fields of death are thrilling to die on, over and over again. The key is asymmetry. Playing a map as the defender gives you a traditional tower defence game, where you plop down turrets and defensive forces to try to stem the incoming tide. Attacking is more like the ‘reverse’ tower defence of Anomaly: Warzone Earth – you decide the order and routes of your units in the hope of breaking through the cyber-Kaiser’s defences.



But what really makes both sides of this top-down strategiser stand out is the unit customisation. Much like Positech’s previous game, Gratuitous Space Battles, you build your own units. Pick a hull and add whatever weapons, armour and engines you desire. Trenches full of riflemen giving you trouble? Put together a heavily armoured flamethrower tank to smoke them out.

But there’s a catch: any unit you design can also be used by the game’s superb, adaptive AI. So that flame tank you treasured as an attacker is now a rolling fortress on the defence. A long-range laser turret will fry an enemy before he gets close, but next time out you’ll have to deploy some heavily shielded mecha-men to take it down. You’re forced into a continual arms race with yourself and, in keeping with the WW1 theme, one you can never quite win.

The campaign is a little on the short side with only a handful of official maps available, but you can browse an abundance of user-made missions. Budding Field Marshalls can edit maps and upload their forces online, custom units and all, for anyone to defend against. The ease with which these challenges can be shared and downloaded extends your playtime immeasurably.



More problematic is the game’s tendency to crash faster than a biplane over Belgium. Starting or finishing a map, as well as saving and deleting units, can potentially result in a short sharp trip to your desktop. You’ll rarely lose any significant progress this way, but it still makes for a frustrating experience.

But these are minor issues that continuous updates will fix, and they don’t take the shine off an otherwise excellent game. Gratuitous Tank Battles is both challenging and strategic, and the clever use of AI and customisation results in a successful bout of experimentation.