Maybe it is just a crossed wire shortcircuiting my memory, but I have a lasting image of an electro-diesel deltic in my old railway memories from a general arrangement drawing, an outline sketch and no more, of an EE half an half.
Even by 1958 it was clear that the deltic with a turbo T18 engine could deliver traction rated power of 2200hp in a very light weight package per power unit, and so using the other engine bay completely for electrical AC equipment and replacing the radiator group at that end with a pantograph.
From EE this would have been in AC form a 3300 bhp continuous output loco with the aforementioned DE mode being ample for dragging 700 tonne trains from the freight rail head, or running 400 tonne passenger expresses beyond the wires of the West Coast Mainline.
Of all power units, the deltic at that time was the only one capable of providing such an enourmous power output per tonne of loco, and basically in being part of the only viable dual mode main line, express speed locomtoive at the time and for the following ten years with the advnet of the high powered valenta.
Why then did this never come to fruition or beyond a sketch?
There are several reasons for this, but basically the need was probably not that well defined at the BTC /BRB. Branch lines were by in large not envisaged for electrification and certainly not many railheads to freight customers. Electrified mainlines though were very much in the plan for a new british railway. Back then we had a different outset than we have today, where trains were still largely marshalled and apart from some coal pit to smelter/power station loads, this meant that several locomotives would be involved with type 1,2 and lower powered shunters haulinbg to the big marshall yards which still stand idle today in a few places like north of Carlisle.
Deltic itself was a ten year 'stop-gap' measure prior to the planned electrification in the late 1960s of the ECML, which ahem meant that the drone of twin napiers went on for another whole decade and was replaced for almost another whole generation by the shrill whine of the IC 125. In another slight irony, deltics in the days of steam heat fairly often ran to Aberdeen on one engine norht of Edinburgh with the slack sections of Fife hardly warranting 3300 hp while perhaps engine hours could be kept down in this way a little. Thus for the reach north as electrification stretched ever more towards Carlisle and Glasgow Central, a dual mode deltic could have provided a reasonable performer even at the non turnbo 1650 bhp rating of a single PU in a dual mode loco.
Another reason there were not more dual mode locos in the first two phases of removing steam locomotion, was that there was rationing of many materials to industry in post war 1950s Britain and for some military materials like aluminium, this went onto the 1960s. Also back then the 25kv AC locos were still not fully proven and perhaps the electrical systems would have had trouble in rectifying and transforming down to the amp /volt ratings of the same traction motors as run by the DE output, I would have to have a check on the types used.
Economics played the part in the expense of proving such a loco, although the successful class 73 demostrates the usefulness of dual mode locos,. in fulfilling different roles even when one of the modes becomes periodically obsolete due to lack of demand or other traction being available or multiple units replacing loco hauled. They find new routes, new types of trains and so on.
Economics foresight should though have played a far bigger part in railway planning, and in fact the nearest we came to an economically self sustainable railway was the full might of Dr. Beeching's dreaded proposals. Wage rises, fuel prices and the accession of freight to long haul road, and personal transport to small affordable commuter cars, on the motorway network could have all been predicted and acted upon by 1960 even.
In harder nosed BTC/BRB relationship, the dual mode deltic could have had a place, as haiuling direct trains to an dfrom railhead to the AC trunk routes and making trains more economic in terms of tractive power allocation, train crews and size of minimum and maximum load tacklable economically. BR missed out on this trick, while the French and Germans did not, and modernised towards larger customers and larger road/to/rail transfer depots, reducing the amount of martialling. In the UK it just died a death with the advent of the tent sided 20 tonne lorry, and later of course, container and tanker traffic to 38 then 40 tonnes.
There have been two big game changers since then in the railway and freight in particular. Firstly, it has remained and expanded its economic superiority to road in large point to point volume freight, and secondly there is now the Channel Tunnel. Now we have super/marhsalling and private railheads acting on behalf of other end users in transfer to road or even in co-location of factories or warehouses to the railhead.
The next game changer is the cost of fuel and price then per mile of in particular, container and small container traffic, and soft sided domestic market containers. Also UK companies will be looking to continue to use scale to competitive advantage and also to supply more to europe as the main market. Added into this is the potential move to several more 'deep' water container terminals, in the SW of England, Hunterston and Aberford in Wales, where monster ships bigger than the 120,000 t "panamaxes" will be able to connect with europe, save a day's sailing and even maybe these will be too big to pass through the shallow english channel at all but spring high tides of a SW swell!
With that type of traffic then a type 3 or just 4 dual locomotive seems a bit underpowered, but dont forget that shunters used to handle trains at low speed from railhead to main line siding. Much of that operation is over with class 66s doing shunts on whole trains and there just being gaps when there was not enough cargo to fill a train rather than the expense of martialling. However then the expectations today are to be able to lift a 2000 tonne train and tommorrows railway will probably be looking at 3000 tonne trains from large scale plants or to distribution centres in order to be most economic. Then you need specialist traction, the heavy diesel type 5 and type 6. This is still why there is so much diesel under the wires, because there is a shortage of electric locos and no real incentibve for using two train crews.
Trains though of 500 tonnes, not forgetting that is upto 20 or 30 lorry loads may become more economic if they are point to point or transconintental, or in plkaces where rail is as fast as road or faster, but much more reliable. Take the tesco use of the highland line, these are only a few hundred tonnes of net freight in the kighter services.
Now it becomes clear that the real use of a dual locomotive for tommorrows railway would not be in frieght necessarily. More likely to be in passenger, where trains of upto 600 tonnes can be managed admirably with less than 2500 bhp and on semi fast routes, 1650 hp would be enough. Deltic through is for now too smokey, so we woul d be looking at the now MAN owned VP series which replaced Valenta , with v6,8 or 12 configuratiion most appropriate.
There are some engine techmoligists researching opposed piston engines for some odd reason, they have mayve kidded themselves on that they are so much simpler that there must be a way of getting them to work within modern emissions demands, and they are allegedly looking into car engine sized opposing four and six piston units in diesel. How they will overcome the inherent smokey issues is yet to be seen. IT could all be like the last great experiment in the 1990s into two stroke, supercharged engines by ford which lead to zero point zero products and profits.
Dual mode in both locos and passenger multiple units is very attractive too either if privatisation is opened to real competition between companies for diagrams on the same routes, whereby those willing to invest in dual mode will gain most on winning cross power source routes or be able to employ their rolling stock on alternative contracts if they do not win their first choice from the list. There is also talk of an under/the(wires levvy for diesel trains in order to encourage use of electric locos or dual mode stock.
On "BR" today even the latest electric locomotives in network use, the class 92 are arguably coming to the end of their economic and safe lifespans. Class 66s are in need of heavy general repair , and the class 60s have already been rationalised. The remaining second generation locos , 47s , 56s and 57s are passed their use by date well and truly. If all pre 1995 ie now two decade old stock and older, was removed then the railwya would run to a hault in terms of passenger services.
There will be some dual and even multimode trains, multiple units and dragged electric loco set ups in the near future, but will we ever see a mainline dual mode Diesel Electric/AC Electro or DC thrid rail?