ALL THREE TOGETHER!
When I received this collection of photos from Tube Troll, I was a little intrigued as to why one 'album' was entitled 'TWAT'! However, on exploration, I find it to be a collection of photos of all three of the trains above together.
I therefore assume that it must mean Tunnel Cleaning, Weed Killer And Track Recording Trains together; at least I'll give him the benefit of the doubt!
Update on this! Tube Troll has enlightened me further on the point; I can do no better than to quote from his e-mail to me:
'On the engineers page, the folder is entitled TWAT because the group of drivers that drive these three trains, and are distinct group seperate from the main engineers drivers group because of the specialist knowledge required to operate these beasts, these drivers are known as the TWAT LINK, for the reason you suspect, the Tunnel cleaning, Weedkilling And Track recording.'
However, they make up a most unusual collection to be seen together at one time!
Captions are unnecessary I think!