Anyone who saw the Omaha beach-head assault in Saving Private Ryan will have an idea of how scary assaulting a fixed, well defended position must be.

The prospect of facing a formidable, faceless menace together with the helpless feeling of being funnelled into a carefully constructed killing zone must have been paralyzing.

Strangely though, one of the most popular casual game genres of recent years has been the tower defence genre, which chirpily makes you the faceless menace. Here it’s up to you to carefully set up elaborate defences in order to repel an attacking force.

Chief among these games has been Fieldrunners, which has appeared on iPhone, PSP Minis and iPad. Now, continuing a popular trend of iPhone conversions, it’s the turn of your little mobile phone.

Check your weapons

The structure of Fieldrunners has always been simple, so it’s not surprising to see it make the transition to mobile relatively intact.

Various types of enemies attempt to cross an initially empty field (or arena, or desert) from one, two or three entry points.

It’s up to you to build a twisting maze of defence turrets which simultaneously slow the enemy’s progress and pummel them into submission. Airborne enemies fly straight over your defences, so it’s important to have a strong spine running the length of the game field.

In Classic mode you face 100 waves with only four kinds of turret – the cheap and cheerful Gatling Tower, the speed sapping Goo Tower, the splash damage-dealing Missile Tower and the super-powerful Tesla Tower.

Extended mode introduces the blanket-coverage of the Flame Tower and the awesome Mortar Tower.

Tactical masterstroke

It’s the carefully balanced combination of these towers - with their trade-offs in cost and area of coverage – and enemy types that provide much of Fieldrunners’s appeal.

Should you spend your money (accrued by defeating enemies) on relatively cheap turret upgrades (two per turret) or save up for a more exotic variant? Do you send your enemies up and down the length of the level at the risk of leaving yourself too thinly spread to repel an aerial attack?

It’s compelling stuff, and the best thing is it’s been made to work brilliantly on mobile. The controls are simple, making great use of keypad shortcuts, and the action moves at a buttery smooth rate for the most part – even with dozens of units on screen at one time.

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It has to be said that the small screen occasionally struggles to contain the action, with the screen becoming cluttered and individual units tough to pick out. On such occasions the overlaid level and money text can become annoyingly obscured.

There’s also the persistent criticism we have with Fieldrunners as a mobile experience – namely its unwavering devotion to 100-wave rounds. Despite a handy auto save feature, it can be a bit of a slog when all you want is a quick, self-contained blast.

Still, that’s no fault of developer MachineWorks Northwest. The commission was to cram an iPhone smash hit into the compact form of your mobile with minimal compromise, and it's done an exemplary job.

Well worthy of a shiny silver medal for excellence in the line of fire.

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