Dont worry about asking Goose - those who dont ask never learn.
So keep 'em coming

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Those Events that have multiple frames are Scenarios. They are on a much larger scale then the weekly snapshot and held 4 or 5 times a year. While some of them also take on "walk ons" (ie players that didnt register and just show up for a frame) you generally need to register for those. The COs of the sides need to know how big their forces are to be able to whip up a battle plan.
The next Scenario is going to be "Battle of Britain" - check the
Battle of Britain 2006 General forum for info. On the
AHevents site you can find more info on what the scenario is about. Its also where you need to register if you choose to take part in the fun. As frames are held in the Special Events Arena, you need to have an active subscription for online play to register for an event. Youll also need to get an account at the AHEvents main site first. Make sure you BBS handle and ingameID are included in your profile, so the COs know who you are when you register.