WW2 Gun Towers in the Thames Estuary Originally connected by walk ways. These where demolished in the 60s after occupation by the Pirate Radio Stations who thought they were outside territorial waters. Some said that they were a good navigational aid for the German Bombers heading for London You can see how big they are almost dwarfing the ship in front of them. You can also just see the wind turbines in the distance behind them.
Those Maunsell Forts were used as a map for German Bombers in The Blitz on London, the Fort you could see Tarkey was the other one not the Churchill Fort [Roughs Towers as we know it] but Knock John, it is on Wiki here
This is part of the Thames Barrier which protects Barking Creek, looking almost like a guillotine, it is designed this way to allow shipping to still enter the Creek to load/offload their cargo at various wharves up the Creek and is only lowered when a flood tide/surge is expected. There are three smaller 'gates' in addition to the main barrier
Whilst on the subject of Barking Creek I suppose most have heard about the battle here involving the engagement of and the shooting down of our own aircraft [Blue on Blue it is called today]