The 3D tower defence extravaganza, Star Defense, was a big game for ngmoco earlier in the year, landing itself a well-earned Gold Award from Pocket Gamer.

Now developer Rough Cookie is keen to show you how the war with the S'rath began, in a free spin-off game called Star Defense Prelude.

The game puts you on the front lines of Outpost D-13 during the very first encounter with the invading aliens. Prelude also offer new recruits the chance to put themselves to the tes ton the Nova Cratos challenge planet, with ten new awards for veterans to unlock.

The original Star Defense game is also due for an update to version 1.3.1, which will then allow players of the original game and the new Prelude to face each other on the Nova Cratos leaderboards.

Star Defense Prelude has already been submitted to Apple, so it should be with us any time now.