It's all fun and games when you're on your iPad, mowing down waves of troops as they march single file down a right-angled corrider.
Try that tactic on a real-life battlefield, however, and you'll find yourself conquered by the first army whose attack plans aren't drawn up on graph paper.
So, to hasten the downfall of our armed forces (and give Apple users some quality titles to play while it's happening), here are the best tower defence games for iPad.
DISCLAIMER: The tactics of military commanders have been in no way compromised by tower defence games. They're all too busy playing World of Goo HD.