Historic steam tug Challenge was re-united with a sea fort it helped position in the Thames Estuary off Kent, 80 years ago to the day this afternoon (August 1).

Knock John naval fort was sunk in the Thames Estuary nearly approximately 20-miles offshore of Sheerness, Kent on 1 August 1942 - one of several forts designed by Guy Maunsell to help defend the Thames Estuary during WW2.

To celebrate Knock John's 80th anniversary, Margaret McEwan - a Maunsell Forts sea forts enthusiast - arranged for the historic steam tug Challenge to revisit the fort it helped position. Ms McEwan was aboard the X-Pilot vessel with members of the Principality of Sealand (itself a Maunsell fort) to mark the occasion.

Challenge was the last steam tug to work the Thames and also helped evacuate troops from the shores of Dunkirk in 1940.

Footage filmed shows Challenge and X-Pilot leaving Sheerness and passing the wreck of SS Richard Montgomery and the Red Sands Sea Forts (also designed by Maunsell) before finally arriving at Knock John naval fort for the historic rendezvous.