Hi Gary

This is fascinating question – in fact I'm currently writing a WWII thriller based on almost the same situation!

Charts I've researched show the Thames isn't deep enough for a u-boat to sail submerged as far up as that part of the river, so it would have to do so on the surface.

Your kids could brainstorm ways they might be able to do that

Meanwhile, here's an inspiring still of the incident the film footage barinasboy linked to – and what got me going on the story in the first place.

[m.allposters.co.uk]

As to defences, I believe there were submarine defences at Sheerness – steel nets which opened and closed to let shipping through. So how would you get through those?

Also, the defences at Sheerness featured some kind of radar capability, but I'm not sure at what point this was installed (more research to do there).

You can even find Sheerness tide table records for the war years to find a high tide – and specific height records – if you think that might be a helpful avenue to explore.

Charts for that area exist online as well.

So, lots of things to find on Google as Cyril has suggested and plenty of problems to solve

Al

Alistair Cox