Well, escort tactics are something that will differ greatly depending on the aircraft. It is very different in may ways with jet aircraft versus the relatively under-powered piston/prop aircraft we use in a game like Aces High. Still, there will be some similarities.
BTW, you should look for "Thunderbolt" by Robert S. Johnson for an interesting look at how the Jugs did their escorts of bombers in WWII.
Ok, there are, in my view, three basic roles you can fill as an escort fighter. You can sweep, high escort, and close escort.
If you have the planes, sending some of them out ahead of the assets to sweep the flight path can be a great escort tactic. If you can engage the enemy threats with fighters before your assets arrive, it is your best chance. Even if your sweepers don't have the numbers or equipment to remove the threat, all they need to do is deflect it. In WWII combat this can mean leading the attacking aircraft down and away from the incoming strike or assets you are protecting. Dragging the enemy lower is very important in WWII air combat, because a prop plane will take much longer to climb back up to your assets. This often will mean that the enemy either can't reach the assets in time, or will run out of fuel before they get there.
The second escort role is high escort. This is an element of fighters that will cruise along the flight path with the assets several K higher than them. Depending on where attack is likely to come from, the high escort can be positioned either slightly behind or in front of the assets and higher. These escorts need to be able to engage fairly quickly using their extra altitude to dive to any attackers and hit them before they reach the assets. High escort is especially important in WWII combat, as these guys will have the extra energy to dive down and intercept the enemy before they are in guns range of the assets. I would think this role would be less important in modern jet combat due to the higher power/weight ratios. Again, fighters in this role need not destroy the enemy, just force or lead them down and away from the assets.
The final, and most important escort role is close escort. The close escort will normally stay just slightly above the assets and in a position to intercept an enemy attack. You ALWAYS need close escort, it is the most important. Where other types of escort can "miss" an incoming attack or leave the assets deflecting an attack, the close escort must always stay with the asset. Close escort will normally be above the assets and within 1k or so, very close. This will mean that no matter what else happens, if the enemy gets to the assets, there will be some fighter elements to counter. Close escort is often the most difficult role, since you cannot get very far from the assets you are protecting. Because you are close support, the enemy may be able to gain a tactical advantage such as altitude or position, and the close escort will be forced to stay with the asset and fight at this disadvantage when the attack comes. The close support fighter must wait until the enemy commits to an attack on the asset, and then move to intercept that attack. Close support pilots need to be very disciplined, and cannot be lead away for an "easy kill". If it comes down to it, the close support pilot must be willing to "take a bullet" it if will stop an attack from reaching the assets.
Ideally, you want enough planes to be able to fill all three of these roles, and have enough planes in each element to counter any enemy attack. In reality, you almost never get enough assets to actually do this. You have to take what you have to work with, and spread it out among the other roles. Generally, close escort is the most important role, but after that it will depend on the situation. For example, if you have a good indication of where an attack may be coming from, putting more fighters into the sweep role may pay off.
If you are interested in this type of thing, you should take a look at the scenario events that are run in Aces High. These type of events frequently feature escort duties, and they are very good learning experience. Plus, there is nothing more exciting than being the close escort and hearing "enemy inbound". Some of the most intense and fun gaming I have ever done has been running escort in scenarios. Check out the Aces High Afrika Corps scenario that will be starting soon. If you like escort, scenarios are the place to be!
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Lephturn - Chief Trainer
A member of The Flying Pigs
http://www.flyingpigs.com 
"My P-47 is a pretty good ship, she took a round coming 'cross the Channel last trip.
Just thinking 'bout my baby and lettin' her rip, always got me through so far."
- Steve Earl
