Great Western Coffee Shop

From Rail Magazine (https://www.railmagazine.com/news/network/2023/02/15/tfl-reveals-first-of-new-b23s-for-docklands-light-railway)


How does rolling stock type numbering work on the Underground?  D76 looks like District line trains introduced in 1976, and the "23" in B23 is, surely, 2023.  But what does the "B" stand for?

On DLR, B is for Beckton depot, and before that P was for Poplar - or so says Wikipedia, and it sounds plausible enough.

Bakerloo line stock?

Conventions vary, so does that mean they're not conventions?

Traditionally the larger sub-surface Underground stock was just letters; I can remember CO/CP, meaning C(onverted) O and P stock, then R stock and there had been Q stock which was really just lumping a lot of odd stuff together. After that the intended introduction date was added and the alphabet started again, so we had A60/62, C69 and C77 then D78. B possibly got missed out because C stock was initially for the Circle line (the second batch was the same but gave enough in total to use them interchangeably to Edgware Road on the District), then D was for the main District line. The latest trains run on all of the Met/Circle/District/H&C sub-surface lines so are S-stock (a nice touch as conveniently S was never reached the first time round, though T was), mostly 7 cars long (S7) but S8 (guess how long!) with a different seating layout for the Met.

The smaller "tube" trains tend just to be referred to as (say) "38 stock" (once on the Bakerloo and Northern lines, now everyone's idea of a traditional red Tube train) or "73 Tube stock", being the current almost worn out Piccadilly line stock.

The B for DLR stock coincidentally hadn't been used in the current round of Underground trains and conveniently linked to Beckton depot, as well as many of them being built by Bombardier, so whatever is written elsewhere I suspect it was a combination of several factors. It's ultimately just a convenient shorthand and having a letter as well as numbers makes it more obvious that it's a reference to something rather than just a number; you can't just talk about a 38 or a 73 without adding some clarification.