moggiee
Notionally the primary threat would be "rogue aircraft" a la 9/11. Quite why al Qaeda would hate the baltic states so much remains a little unclear!
In reality, its a comforting gesture from NATO to our new converts to show them how warm and cuddly we are on this side of the old iron curtain.
The reason the guys are only there for 3 months is because noone is willing to stump up for full coverage until 2006 when the 3 countries hope to provide their own air defence. So we end up rotating the duty around NATO members with the massive additional cost involved of each nation having to set up its own logistics and support system every 3 months ...and all this is meant to impress them?