An easy-to-navigate menu lets you queue units or call in reinforcements from anywhere on the map, and building your bases and commanding your soldiers is as easy as pointing and clicking the mouse (you'll need to use a few keyboard commands, as well).

CNN: Review: Command & Conquer: Red Alert 2

This margin depends on the size and speed of an aircraft, and re-ordering the queue can minimise the delay before all the planes get into the air (mathematicians call this the departure problem).

ECONOMIST: Algorithms