Bit short notice here...
F100 Class destroyer Mendez Nunez (F104) is heading upstream on the Thames (24 April, 1700 BST), fresh from finishing her part in Exercise Joint Warrior 15-1.
http://www.helis.com/database/unit/201_Mendez_Nu%C3%B1ez/
Not sure where's she's being berthed yet - not in Port of London published movements and unlikely to be beside HMS Belfast (not in Tower Bridge lift schedule). Not sure if there's an embarked flight, either.
More when I know.
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Update 1: Headed for West India Dock (thanks, @NavyLookout). Nearest station: DLR South Quays.
https://www.flickr.com/photos/dyvroeth/16656324783/
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Update 2: SH-60B HS.23-09 01-1009/09 ranged on the flight deck.
https://www.flickr.com/photos/dyvroeth/17274768462/
Ship open to the public on Sunday 26 April 2015