In 2013 it became apparent that the new Siemens Desiro City stock (Class 700) for Thameslink would not be available in time to release Class 319 units to Northern and London Midland. The pragmatic solution was to order 29 new 4 car units as interim stock for TSGN, the Invitation To Tender (I.T.T.) being issued on 26th September 2013, with the first delivery scheduled for October 2014. Built into this requirement was that this fleet would be cascaded elsewhere when no longer required for this temporary commitment. These units would be designated Class 387 and would be the first to use a new six digit car numbering scheme. With such a tight timescale it was implicit these trains would need to be as near as "off the shelf" it is possible to get with rolling stock. Thus Bombardier was awarded the contract for their final iteration of their successful and numerous "Electrostar" units. (Thereafter Bombardier production would switch to its new "Adventra" range. The Electrostar range could not continue indefinitely because of impending new, more stringent about front end collision protection, regulations with which they would be non-compliant.) Class 387 units would use the later Electrostar bodies with discrete windows (and other new features) first seen on National Express East Anglia Class 379 units, then Southern's Classes 377/6s and 377/7s. The reason these new trains would not be designated a sub-class of 377s is because they additionally would have new, different and incompatible control software, have a maximum speed of 110mph and be ETCS-ready.

As will become apparent throughout this article nothing is simple nor static about cascades involving Thameslink stock! Because existing Thameslink unit diagrams involve much joining and separating of units during a day, 387s could not just be introduced onto Class 319 diagrams on a unit for unit basis, so Thameslink diagrams would need regular changing as 387s (and subsequently 700s) were introduced. Bear in mind at various points in time Thameslink services would be run by Classes 319, 377, 387 and 700, all of which are incompatible. Furthermore it was not just 319s that needed to be released as Thameslink had borrowed six 377/2s from Southern that needed to be returned for Southern to cascade some 377s, not necessarily the same ones, to Southeastern. Then in October 2014 throw into the TSGN pot that it was decided to replace the Class 442s on Gatwick Express services. Whilst many regard 442s as the most stylish, smoothest and comfortable Southern Electric units ever, they were designed and built as long distance trains and are not suited to the relatively short intensive nature of Gatwick Express services. A further 27 Class 387s were ordered on November 18th 2014, using up 108 of the 140 available carriages from the add-on order provision for 387s. These were designated Class 387/2, the Thameslink interim stock becoming Class 387/1.

387101 was hauled from Derby to Ashfordby for testing on the Old Dalby complex the afternoon of 15th August 2014. It was decided London Midland's Bletchley depot was to be used as base for mileage accumulation, with mileage accumulation being between Willesden and Crewe, and Bletchley and Brighton. This would eventually, getting somewhat ahead of the story, apply to all 387s built, not just those for Thameslink and Gatwick Express. AC testing between Wembley and Crewe commenced 9th November, DC testing to Brighton 10th November 2014. Of really important note, unlike the tortuous introduction of other new multiple units of this era, 387s worked reliably pretty much straight out of the box. The history of British locomotive and multiple unit procurement and production since the inception of railways is liberally littered with a large multiplicity small batches of numerous types, many of which were not successful. The Electrostar range has benefitted considerably from large scale production over seventeen years with its accompanying experience and continuous improvement. Thus being more akin to diesel locomotive development and production in North America.

Class 387s would be allocated to Lovers Walk. As a result all 377s there would be re-allocated to Selhurst and as a knock-on 455s to Stewarts Lane. On 3rd October 2014 unit N°387106 was the first unit delivered to Lovers Walk. This unit, with unit N°387105, were the first to enter service, running the 2T02 05:50 Brighton to Bedford on 7th December 2014. From this point it was expected that eleven 8 coach trains would be diagrammed from 7th April 2015 (10 on Sundays). Followed by 24 units diagrammed from 18th May 2015. The last two 387/1s entered service on 24th June 2015.

Unit N°387201 was delivered from Derby to Bletchley on 12th October 2015. Along with N°387202 it did its AC mileage run on 9th November and DC run to Brighton the following day.

On 2nd November 2015 it was revealed that Porterbrook had speculatively ordered 20 Class 387 units "for lines to be electrified" for delivery between October 2016 and June 2017. Of which more, later.

Thameslink stock changes from December 13th 2015 resulted in the only 12 car workings being 387s, though this was not the same three units coupled all day as the practice of unit joinings and separations continued in diagrams.

From Wednesday 27th January 2016 387/2s were cleared for the Thameslink Brighton - Bedford route. Accordingly unit N°387201 entered service as the rear unit of 1W02 05:30 Brighton to Bedford on the 2nd February. Further 387/2 introductions were on Thameslink services in the company of 387/1s, due to a programme of 387/1s returning to Bletchley for further attention. The 29th of February only comes around once in four years and in 2016 is was extra special because on 29th February 2016 387/2s commenced Gatwick Express services with units N°387211 and N°387207 on the 18:26 Victoria to Gatwick. Class 387/2 units ceased routinely working Thameslink services in September 2016. The last Gatwick Express 387/2 unit, 387227, had entered traffic by 7th July 2016.

It is not the intention to cover the lives of 387s away from the Southern in any great detail here, and in Southern circles the use of the initials "G.W.R" can be regarded as something approaching heresy, however it is necessary to go into a little detail for historical completeness and in connection with unit cascades. It had been previously decided that after Thameslink use the Class 387/1 fleet would be handed-down to GWR to replace Networker Turbo DMUs on Thames Valley local services after their lines had been electrified. Twenty nine units would be insufficient so GWR took up the option on the remaining 8 follow-on units, originally due for delivery between October and November 2016. It was also planned that the balance of the required number of units would be made up of half of the Class 365 fleet released from the GN. However, on 26th April 2016 Network Rail published a GTR vehicle Change Proposal for the twenty nine 387/1s to be instead transferred to their own GN services. This making a lot of sense over the previously proposed Class 377 transfer given the 387s' 110mph top speed and ETCS readiness along with future requirements for the ECML. On 15th June 2016 387106/14 were transferred to Hornsey 15th June for staff training. Passenger workings on the GN started on Monday 10th October 2016 by which time 387104/106/109/110/111/112/114/119/120 were available. By 1st December 2016 only 387101/103/105/115/118/121/122/124/127 remained on Thameslink services. The final working on a 387/1 on Thameslink does not appear to have been recorded but it was earlier anticipated all would be working on the GN by February 2017.

Tracking back a few months, in mid-May 2016 it was known that the eight option 387s for GWR would be completed by the end of the month and the twenty speculative units for Porterbrook by the end of the year. c2c were in need of additional capacity to supplement their early Electrostar Class 357 fleet, so they took out a lease on six of the speculative build. The remaining fourteen of the speculative build were taken up by GWR to in-part compensate for the loss of the twenty nine from GTR. Further to make up their 387 fleet GWR ordered another twenty three to take the total of forty five; to have a unified all-new Thames Valley fleet of fewer units and no longer require the hand-me-down 365s. Because the build of 387 units would then go beyond the change in regulations all the cabs for the remainder of 387 production were constructed before the deadline.

Note that all 387s running entirely on ac retain their dc capability including shoebeams and retractable pick-up shoes. Therefore, as mentioned before, the fleets for GWR and c2c did dc mileage accumulation on the Southern. The first for GWR, N°387130 and 131, doing so to Brighton on 14th July 2016. The first for c2c, N°387301 and 302 were due to run south of the Thames on the 13th October 2016 but this was terminated at Wembley and changed into an AC run to Crewe. They were subsequently run on the Southern.

The Class 387 can be described as a competent and capable, if un-remarkable, modern dual voltage mid-range units. They are only let down by their desperately uncomfortable seating, which is not the fault of Bombardier but of those who specified it. Thereafter Class 387s have settled down on Gatwick Express, Great Northern c2c and GWR services and the "Fat Controller" might describe them as "Really Useful Trains".

Gatwick Express unit N°387219 was damaged in a sideswipe incident with a Class 455 (at Stewarts Lane???) and returned to Derby for repair between early July and 28th July 2017. For quite a time Gatwick Express had a single unit back at Derby for rectification work so N°387105 was temporarily transferred from the GN between 24th October 2018 and 16th May 2020, bringing back the sight of mixed coloured formations.

The Global Pandemic in 2020 led to a major reduction in services and there were so few flights in and out of Gatwick Airport that a dedicated airport service was not required. The complete withdrawal of Gatwick Express services additionally assisted with the major rebuilding of Gatwick Airport station (which had commenced prior to the Pandemic), where platform capacity had become limited. The red 387/2 fleet was redeployed on regular Southern services including between Brighton, Hastings and Ore. In 2021 it was announced that TSGN's entire Classes 377 and 387 fleets would be upgraded under "Project Aurora", the much older 377s being treated first. In due course 387201-6 had their vinyl Gatwick Express branding removed and were transferred to Hornsey depot for use on TSGN's GN services, and at a time of reduced services this permitted complete withdrawal of GN's Class 365 fleet ahead of the original plan. Longer term, additional 387s on the GN will assist with Project Aurora refurbishments of the GN 387/1 fleet. However the aluminium cracking crisis afflicting LNER's and GWR's IETs fleets in 2021 left GWR significantly short of serviceable trains. Initially c2c's 387301, 302 and 306 were transferred to Reading depot, then in July 2021 red 387201-6 were transferred to GWR (204-6 on 13th July, 201-3 on 20th July). They were replaced on the GN by 387207-9, three additional units by then known to be sufficient for the reduced Kings Cross services.

Fleet and Technical details:

Unit deployment
387101-129 temporarily TL, were going to GWR but subsequently changed to GN
387130-174 GWR new orders (subsequently 130-141 to HEx with ETCS installed)
387201-227 GEx
387301-306 C2C from Porterbrook, lease 5 years from late 2016

Unit formation:

DMC  MS  PTS  DMS
2-bo  2-Bo  2-2  Bo-2

• Bombardier P3-25 and T3-25 bogies
• Bombardier asynchronous 250kW traction motors
• Disc and regenerative brakes
• Pickup 25kV overhead, 750v DC conductor rail retractable shoes
• New type of high speed Bracknell Willis pantograph for sustained high speed running
• IGBT inverter control
• Maximum speed 110mph, ETCS ready
• Dellner 12 couplers - can work out of service in an emergency with Class 377
• Aluminium alloy underframe sides and roof, steel and GRP cab ends, bolted together
• Gangways at ends and narrow throughout
• Sliding plug doors
• Air-conditioning, Wi-Fi and PIS
• Seating = 2+2 facing and coach