Raiding
A raid is normally a small to medium fast attack. The aim of a raid is not to kill or cripple an opponent, but to sap his strength, and to distract him from building his economy.
Raiding is typically done with smaller groups of fast units, with at least moderate damage potential. The idea is to use speed and surprise to avoid defences and destroy some economic buildings. The most popular target for a raid is the metal extractor as they are easy to kill, and metal is generally the critical resource. Windmills are also easy to kill, and if enough are destroyed, the resulting energy stall will hurt the defending player badly. If the enemy's built his windmills too close together, they can also chain-explode, seriously damaging his economy. Construction units and factories are also worthwhile targets, although generally a raid will only take out a factory if the defence is very slow to respond.
As the game progresses, raiding generally becomes pointless due to the accumulation of defensive structures and gradual closing-off of open approaches. A raid against a well defended position will only waste resources and give the opponent metal wrecks to reclaim. However certain specialist units such as hovercraft, amphibious units, stealth units, and all terrain assault kbots may be able to cover difficult terrain or slip under radar cover, allowing a surprise raid from an unexpected direction much later in the game.
Raiding should be used with care against a porcing opponent. You should raid just enough to encourage the porcer to stay behind his defenses, allowing you to spread across the map and take control of as much resource as possible.
In many TA based-mods, air units are not normally built early due to their high cost but are very effective against ground units that are not designed for anti-air fire. As a result there is often an opportunity for an air raid in the mid game, after ground defences have become established, but before anti air defence is solidly established. This means that it's usually a good idea to start with a Vehicle or KBot factory (depending on how flat/rough the terrain is and how much metal you can get your hands on) and put down an air factory before or just after your first L2 factory. This can also help protect you against air raids, as the L1 fighters in most TA-based mods can quickly destroy L1 bombers and gunships.
Good radar coverage is vital for a successful raid. Without it, you will likely stumble into heavy defences or concentrations of units. With it, you can steer your units away from large concentrations of enemies and pick off outlying structures and units. Early on, the only real form of mobile radar in most TA-based mods are the easily-destroyed recon planes, though recon cars like the Jeffy/Weasel and recon KBots like the Flea can fill a similar role.
Good radar coverage is also important for defending against raids. Radar will usually give early warning of an approaching raid, allowing you to mobilise defensive forces to respond. Light defensive structures, like LLTs or mines, are also useful. They don't necessarily need to be heavy enough to stop an attack dead in its tracks. It's enough to slow an attacker down, damage his units, and tip the odds nicely in your favour when your combat units arrive to engage the invaders.
