Having lived in Plymouth, I recommend the Crownhill Fort
http://www.palmerstonforts.org.uk/pav1/plym.htm
it has working cannon. ahh.. nostalgia. At one time I had a dozen copies of the free tourist guide to this place. It was an outpost of the Royal Marines in my Morrow Project (or rather Atlantis Project) game
If you have forces in Plymouth (South Devon) they should really make a quick trip to Umberleigh (North Devon) and have a word with the owner of the Cobbaton Combat collection. Alternatively, RAF Chivenor might make a visit
http://cobbatoncombat.co.uk/
The website's pretty lousy - but it does show some of the vehicles. A Sherman and - I think - a T34.
I don't know how desperate the Royal Navy might be, but there is another Sherman just up the coast at Slapton Sands in Somerset. It IS a memorial , but that might not stop them
http://www.shermantank.co.uk/recovery3.ikml