Anyone know what was tentatively assigned the "missing" Class 509?
It was allocated for new Merseyrail EMUs for extensions such as Kirkby - Wigan Wallgate and replacements for 503s north of the river
My recollection is as follows.
The TOPS numbers in 3XX series were allocated to AC and dual voltage sets, 4XX to ex Southern Railway and Southern Region sets with numeric-alpha identification codes, and 5XX to all other DC sets; thus 507s and 508s were allocated to the DC sets built to the then new BR standard design of EMU with two power cars
507s were built for Merseyside to replace 502s, and on all internal BR documents I remember seeing the 508s were always intended for SW services out of Waterloo, hence their construction as 4-car sets
When the Northern Merseyrail line was extended to Kirkby, class 503s were transferred to work it from the Wirral; there were also plans to extend it beyond Kirkby to Wigan Wallgate, together with some other extensions, and after discussions between BR and Merseyside PTE (or whatever it was called at the time), the PTE agreed that they would underwrite an advance authority being given to GEC for more electric traction equipment; these would power the class 509s, which would replace the 503s north of the river and operate extensions such as to Wigan Wallgate. Then the PTE withdrew its underwriting of the advance authority
By this time, BR had already decided to change to its next generation of EMUs and 317s with there 20m long Mk III based steel shells and a single power car had already been ordered for the BedPan electrification scheme. BR got the necessary authority to build what were classed as 510s - basically 3rd rail DC versions of the 317s - and the advance authority given to GEC for 509s was converted into one for these 510s. This was for complete sets of traction equipment; using parts recovered from SUBs or EPBs (including EE507 traction motor armatures) came later.
Rather than have a mixture of 508s and 510s on the Southern and 507s plus something like 510s on Merseyside, it made sense to concentrate 507s/508s in the north, and build replacements for the 508s down south. However, only 3-car sets were required on Merseyside, and so some 455s (as they'd now become) were built as three new cars plus one ex class 508 trailer; to see what a combination of different rooflines would look like, a new 317 trailer (built at Derby) was marshalled in with three low roofline vehicles. I never did learn why it was done in reverse to the planned combination.
We are, of course, talking about events which happened 40 years ago, and so the above summary might be slightly incorrect, but it is how I remember it; and I'm writing this as someone who was involved.
Another example of the Southern's "stuck in a time warp" mentality where auto-couplers were deemed too new fangled and dangerous. The same mentality meant they were still building Mark 1s with doors to every seating bay well into the 1970s.
It wasn't as simple as this!
Go back to winter 1966/7 and Doncaster built a wooden body with sliding doors on an old 4-SUB frame; it was placed alongside a withdrawn 4-SUB trailer, and on a Saturday morning staff were encouraged to visit the works with the families (and I believe they were suitably rewarded with free food!) and there were trial loadings and unloadings of the two vehicles. The interior layout if the wooden mock-up was then changed, and the test was repeated the following Saturday; this continued over a number of weekends, and what was deemed to be the optimum interior layout was identified.
This wooden mock up was then converted into the PEP prototypes, and these had Scharfenburg automatic couplers; but there were so many curved platforms and sidings on the Southern that I was told that they proved to be worse than useless.
Buckeyes had been used for years on the Southern, and so BR decided to try the Tightlock form the same general family; to this was added what was sometimes called the "Preston Box" - the electrical connectors to assist with automatic coupling, The 508s had these, but there were still problems on the Southern, and so there was the change to the partially manual coupling arrangements found on the 455s/456s/442s,