A detailed and most interesting article.
I just saw the end of steam in Cornwall and recall at a young age being told that Kings were too heavy to cross the Royal Albert Bridge (RAB) so had to be removed at "Plymouth". So logically non-stop trains must have had a Castle all the way from Paddington, mustn't they? However, in the late 60s I started buying old BR publications from which I learned that non-stop trains had made an unadvertised stop at Devonport to remove the King. Clearly "Plymouth" wasn't "North Road". Research was required. The Working Timetables confirmed that Kings were not permitted onto Weston Mill or Royal Albert bridges. However, there was hearsay that Kings worked empty stock to RAB loop on Summer Saturdays. There is also anecdotal evidence of Kings being tested into Cornwall in the 1930s but nothing apparently came of it and I'm not aware of any photographic confirmation.
The Working Timetable is quite clear: "Engine Restrictions - Totnes to Keyham (inclusive) - All types authorised. Keyham (exclusive) to Penzance - All types authorised except 60XX, 47XX and 71XXX. At Devonport, 60XX prohibited in sidings. At Keyham, two 60XX may back into Admitalty Siding but prohibited beyond Barrack Gates." Seven minutes were allowed for an engine change at Devonport, so I surmise that: (i) Castle runs Light Engine Laira to Devonport and backs into Siding behind Signal Box; (ii) King arrives with Paddington train, detaches, runs ahead to Keyham, reverses into Admiralty Siding; (iii) Castle emerges from Devonport Siding, attaches, hauls train to Cornwall; (iv) King emerges from Keyham Siding, runs Light Engine to Laira.
Up trains were allowed 6 min to change engines at Laira Junction. It was normally taboo to make passenger shunt moves on a main running line so this must have been fairly unusual, and I wonder why it couldn't have been done say at Keyham where there was an Up Passenger Loop. Presumably North Road was too congested to stop in the Middle Road.
Turning to Bryn's specific questions, where I've said "Castle" above, this includes Counties, while lighter trains might have a Grange or Hall and heavier trains might require double-heading or banking. If a second loco is needed for the South Devon banks, it makes sense to double-head from Cornwall to Newton Abbot rather than stop in the Plymouth area to attach the assisting engine and then stop again at NA to detach it. If the train were advertised non-stop at NA it would stop in one of the non-platform lines away from the main station.
The WTT has a footnote for each train, for example: Where this train requires assistance, the assistant engine to go through from Newton Abbot to North Road (Down Trains) or from North Road to Newton Abbot Station (Up Trains) or Newton Abbot West Box (Up Trains not stopping at Newton Abbot Station). Trains were allowed 4 min to attach or detach the second loco at NA. Otherwise, assisting engines would be detached at Rattery on the Down, or Hemerdon on the Up, but by running through to the next major station it saved time and finding a path for a light engine movement.
Two locos were permitted to run coupled together at the head of a train, but between Laira and North Road upto five could run coupled together at reduced speed to save loco paths. Mannamead Signalbox may have been one of the smallest but it was open continuously and said to be one of the busiest on the region.
The standard weekday service saw all passenger trains (except ECS) calling at North Road, with the Cornish Riviera then calling at Par, Truro, Gwinear Road, St Erth and Pz. In the early 50s the Riv and Sleeper were hauled by a Laira Britannia west of North Road, but in the mid-50s they reverted to Castle haulage. (Does anyone have photos of Britannias in Cornwall?)
However, in Summer all this changed with Fridays seeing relief and overnight trains, and on Saturdays the Riv running in two or three parts. The timetable changed over the years, but a typical Summer saw the main train non-stop to Devonport to change engines, then Truro, St Erth and St Ives, a second part calling at North Road and main stations to Pz with a portion for Perranporth, and initially a third part splitting for Kingsbridge, Newquay and Falmouth. After the war the service was spread out by transferring the third part to a dedicated Newquay train at 09.30 ex-Paddington and the Falmouth combined with the Pz. (When did the Kingsbridge portion cease?) In the Up direction the service was not symmetrical, with the Perranporth and Falmouth running as full separate trains.
On Sundays there were so few trains that the Riv served most major stations and didn't have any interesting operational characteristics.
Although the majority of Kings were allocated to Old Oak, Stafford Road and Laira, there were occasional allocations to Bath Road, Canton and Newton Abbot. It's unlikely that the timetable planners would have wasted a path for a Laira King to come up light engine to NA to take over an Up London service, so it's more likely that the King came up on a short working or came down on an earlier train from Paddington or even arrived the previous day. For a time on the Down, the 10.30 Pad shed its King at NA for a pair of Halls, and that King then double-headed a second King on the following 10.35 Pad from NA to North Road. The pair of Halls on the 10.30 ran non-stop from NA to Truro where the train split into St Ives and Pz portions of which the two Halls took one portion each
As train speeds increased, stops, timings and vehicle loadings could be adjusted to improve stock and crew efficiency - the Britannia diagram mentioned above achieved 300 miles per day* - but steam loco availability was quite low - a loco might make only one trip a day and spend the rest of the time Spare on Shed - so there could be a temptation to send a spare King out and keep the more versatile locos in reserve for lesser services. The Up Riv arrived at Newton Abbot around 1pm and the Down Riv left around 2pm so in theory the two Halls could have returned to Pz, but I suspect that fresh engines were made ready - management didn't want to risk delaying their crack express. That said, even with 40 min extra being allowed from Plymouth to Paddington for congestion on a Summer Saturday, horror stories abound about two-hour delays between Taunton and NA on Summer Saturdays when management were themselves on the beach meaning that disaster recovery fell onto District Control and local Stationmasters.
The 08.15 Perranporth and 08.35 Falmouth changed engines at Laira Junction but also had an assisting engine to Newton Abbot. At one stage, the Perranporth had a dining car for the whole journey, but the Falmouth dining car was attached at Truro. The 10.00 Newquay diner was advertised non-stop from St Columb Road to Paddington, but loaded to 15 coaches so had a pilot from there to Par, changed engines at Laira Junction and had a second pilot from there to NA. At this stage the main Riv was the 09.20 St Ives which did call at North Road.
The Kings were early casualties of dieselisation but ironically about ten years later the RAB was upgraded and Kings can now reach Cornwall legally. About the same time, the line was singled from St Budeaux eliminating the weak-looking Down Line bridge over the Southern. (Was any work necessary to Weston Mill Viaduct?) However, I'm not aware of any King using the upgraded route into Cornwall until the railtour of 9th May 1998.
Some associated issues are raised by the Working Timetables:
During WWII longitudinal sleepers were placed between the rails over the RAB to allow military road vehicles to drive across in emergency. These were signalled as a train using a pilotman and token. Were any such moves ever made?
Why were 47XX banned from Cornwall? Although they had a longer wheelbase, their Route Availability was Red, their Minimum Curve and Load Gauge the same as a Castle. They were used on Paddington expresses to supplement the main fleet, but were limited to 60mph.
Interestingly, a freight timing load is given for West Country Class Newton Abbot to Truro, although I'm not aware of any WC using that route until the PRC railtour of 3rd May 1964.
Another note says that when a freight is assisted from Tavistock Junction to Redruth, only one engine must steam when passing over the Royal Albert Bridge. This is presumably to reduce the hammer blow effect on the structure.
Gas Turbine Locomotives Nos 18000 and 18100 were cleared to Keyham, but as there are no instructions for them west of Keyham I assume they were banned from Cornwall.
As of 1957: "In emergency the 2,000hp Diesel hydraulic locomotive may proceed between Cowley Bridge Junction and Devonport Junction via Meldon Junction provided it is not coupled to any other locomotive when passing over Meldon Viaduct at 199m 41ch." As it refers to locomotive singular I assume it means D600 which was delivered at about that time.
*Compare that with an HST or IEP which might do 1.5 return journeys between Pad & Pz, c900 miles. Those with long-range fuel tanks might do even more.
(For more detail on locomotive-infrastructure compatibility, go to Cornwall Galleries > Newham Branch and scroll down to "A Technical Viewpoint".) John Roberts.