If you wish to know more and see a photo of the Osprey (which I also saw that evening) then try this link:
http://www.islandecho.co.uk/news/army-exercise-gets-underway-on-the-isle-of-wightThough I think that Mike might have come across some of the related info (with his interests in the Yarmouth Gig club) esp.
"Troops and vehicles arrived on the Island overnight and throughout today with several coming into Yarmouth Harbour on a mexifloat. THE BRITISH ARMY WILL LEAVE ON WEDNESDAY 9th SEPTEMBER VIA YARMOUTH HARBOUR."
-hope the gig isn't scheduled to go in/out at the same time!!!