Theres an RAF Base at Northolt as well. thats even closer to London.
If they was to do a forces day, they should have IMO done it for the Celtic game as thats on 6th June (as we all know) and could have based it round D-day and all that. Plus maybe buckets on gates for Help the Heroes.
could if time it right in Sept,do the same thing and base it round Battle of Britain for the sevices.
And just do what mickyb said and get them to show ID at gate,get half price ticket, could really just have 1 gate for them in ground thats not nomrally open for this (i.e Lexus Stand end), could go as far as to give them a raffle ticket intitleing them to one free beer.
And as an ex serviceman i can tell you once you had a free beer you go back for more.