Construction of two 16 wheel Navy KUA Flask Carriers for use with The DRS Class 57 pair and mk2 DRS escort coaches



This page shows how a model of the 16 wheel Royal Navy KUA flask carrier was produced, using two Dapol KTA container carriers, plasticard sheets, styrene pre-sectioned extrusions and a bit of imagination. 

While researching freight trains incorporating the standard nuclear power station FNA flask carriers in preparation for the completion of my two DRS Class 57 locomotives, I came across some You Tube video clips showing Class 57 pairs towing much larger flask carriers, with two Mk 2 DRS coaches in the rear.  The information with the video clips and corresponding photos I have found subsequently on the web suggests that these relatively infrequent trains operate between Devonport and Sellafield in connection with the reactor fuel used by nuclear submarines.  This looked a bit more interesting than the power station trains and next I discovered that the two DRS Mk2 escort coaches were still available as a limited production run by Bachmann for Model Rail Magazine. So by early in 2012, I had two DRS Class 57s and the two coaches.....all I needed was a pair of KUA flask carrier wagons. (Not a likely subject for a ready-to-run model and not a unit available in kit form .... as far as I know.)


The two Bachmann DRS 57s plus escort coaches with a temporary stand-in FNA flask carrier........


.........BUT...... Something more like this is the objective!


YouTube video clips:

Click on the YouTube links below to see examples of these rather special trains:


There are also several photos on the web, which can be found using Google images and suitable key words.


The KUA Model starting point:

I needed two twin bogie donor rail vehicles to construct the 8 wheel bogie assemblies at each end of the KUA.  I selected Dapol KTA container carriers, having established that the bogie style looked similar and the container holding well sides had some resemblance to the central well girders of the KUA. They also conveniently included a pair of handbrake wheels and Hatton's had stock! (I also gained two more 40 ft containers per KUA).

Dapol KTA Wagon (High Cube containers go to the stack in the container terminal).

(Picture copied from Hatton's Website at



Establishing the dimensions:

The good news:   I came across a photo on the web, showing a near perfect side view of a KUA wagon coupled to a Class 66 locomotive. The Class 66 dimensions are well documented, so with some careful measuring of the enlarged screen display and a bit of simple arithmetic, I was able to calculate the 1/76 scale lengths and height of all the major elements making up the KUA wagon.  One of my scaling sheets is shown below. 


Example of original scaling photo

Part of the angular correction drawings

The Bad News:

I made my first model based on dimensions that did not take account of the shortening effect of the small angle presented by the Class 66 loco to the camera viewing axis. I also omitted to take account of the small effect due to perspective on the relative height of the Class 66 and the flask carrier.  The consequence was a model that was too high and too long.  It looked pretty good until I coupled it up to the Class 57s and escort coaches for the first time. The errors weren't huge, just a few mm in height and 2 cm or so in length, but it was very definitely, "back to the drawing board".

I made a few scale drawings based on the scaling photo and soon discovered the source of the problems. The KUA dimensions were around 7% too large. Applying the corrected dimensions, I set about building a second model: The dimensions quoted below are in line with current estimates.



Note that the smaller pictures below can be enlarged by clicking on the image.

The Bogie Assemblies:


The bogie pivots and buffer beam were cut from one of the KTA wagons. These were connected together with a reinforced 2mm plasticard "T-section" beam.

"T" section beam used to bridge between bogie pivot points


Top view, on the KTA bogies


Cross beams and platform above outer bogies:

A cross beam was then inserted at the central pivot point, which is a little closer to the inner bogie than the outer. The tapered cross beam with lifting eye, above the outer bogie was also fabricated from plasticard and attached to the main frame sides directly above the bogie pivot point. The upper platform was fabricated using plasticard sheet. The railings were made from 0.9mm diameter plastic rod, bent at the outer corners after heating over the bit of a soldering iron. An M2 size nut was embedded at the central pivot point, with a piece of 1mm sheet plasticard (incuding the small screw hole) glued over the top. The handbrake wheels were cut from the KTA wagon and superglued to the appropriate point on the inner bogies.  Some brake components were also cut from the KTA wagon and added for a bit of inaccurate interest under the platform and under the pivot point.

Dimensions used were as follows:

Bogie centre separation: Should be 63mm (but a little longer at 66.5mm on the model to compensate for shorter bogie axle spacing)

Height of the top of the platform above the outer bogie, above rail tops = 25.7mm. So, as the measured height of base platform over outside bogies = 16.2mm, using 1mm plasticard for the upper platform, the spacer height = 8.5mm.

Top platform length = 45mm; width = 10mm.   Railing length = 44mm. Height of top rail above platform top  = 15mm.

Small end platforms: 1mm base. Railings 32mm long & 15mm high.



M2 nut embedded into the central pivot point.

Platforms and cross beams in place.


Handrail assemblies from 0.9mm plastic rod



Handrails & Spurious KTA brake parts added

Central pivot cross beam shifted closer to the centre section


Back on the bogies, buffer beam steps & handbrake wheels fitted


Both bogies ready to paint


An initial coat of paint was applied, using Humbrol 25 blue, 27 grey, 154 yellow and 34 white plus a mix of aluminium metal cote & 27 for the buffers (no steel metal cote available)

NB: My elderly Humbrol 25 was about right, but new Humbrol 25 is darker with a hint of purple...... It can be toned down to about the right shade, by adding Humbrol 89 mid blue.


Initial coat of paint


On the Bogies again




The original central flask structure:

I found an "I" section plastic beam sized at just over the correct height, to model the main flask carrier beams on each side of the central flask cover.  A part of the KTA wagon side panel was used for the well beam below the central area of the flask wagon. The rails for the flask covers, suspended from the side beams were "L" section, 2mm high & 3mm wide, using 2mm x 2mm plasticard L section and a slightly wider strip of 0.25mm plasticard.

Main dimensions used:

Main girder length = 195mm ;  Extension girder length (at each end) = 12.5mm ;   Flask cover rails length = 172mm.

Well girder bottom length = 67mm ; Well girder length at bottom of cover rail = 89mm.

Flask cover length = 98mm ; Flask cover side height = 23mm (later reduced to 22mm, when slightly shallower main girders replaced the originals); Flask cover curved roof  height = 13mm.



The main centre section building blocks with Well girders cut from the KTAs

I beams bonded together with cover rails & end pieces fitted


End floor sections fitted



Girder end pieces added


Central well underside plated in

Ballast weight screws super-glued in

Cover rail brackets fitted







The end bogie assemblies are attached to the central flask carrier:

After painting, the centre section is fixed to the bogie assembly central pivot points using a size M2 bolt at each end, through 2mm holes and spacers in the underside plasticard of the central assembly ends.   In case future adjustment or dismantling of the bolts is required, the decking above the bolts is not glued in place. Instead, it is a tight fit, held in place by the paint applied over the entire deck. (The decking pieces can be levered out with only minor collateral cosmetic damage if this is required.) 

Bogies and centre section bolted together & deck painted

(First model in the background)



The flask covers:

Although I haven't seen any pics of the very heavy nuclear fuel carrying flask, carried by these wagons, I guess it must be a horizontal cylinder in shape. The flask covers completely hide the metal flask. The covers appear to be made in two parts, with a break around the centre line. To allow access to the internal flask, the cover fixing bolts are released and the covers are pulled apart, running on the L section rails, fixed to the side of the wagon on brackets.

First the roof:


The roof internal structure

(making those roof ribs takes quite a while)


After adding the stiffening beam, a thin sheet of

plasticard is glued & folded around the ribs and base edge.




The plasticard is first glued to one edge. When this

has dried, glue is applied to the other edge and the rib tops.

Then the assembly is rolled, inverted over a flat surface,

to bond the plasticard to the frame


Next the sides and ends:


After the overhanging excess roof sheet is trimmed to size,

the sides and ends of the flask cover are glued in place




Any excess roof width is filed flush with the sides

And a coat of pale grey matt enamel paint is applied


The split between the cover halves is marked down the centre line in pencil.

The side and end vents are drawn on the PC and printed on to thin paper. After cutting out, they are glued in place.

The handles and locking bars are made from plastic rod and glued in place.

The top vents are applied using a black marker pen.




The complete Navy flask train in its original form.


Subsequent KUA centre section modifications:

The centre sections have been rebuilt with slightly thinner 11.1mm Plastruct main beams, which gets the overall height about right. The construction technique was changed to accommodate sections cut from the donor KTA wagon's side plates that include the TOPS data, on the sides of the main beams. New well beams were then fabricated to include the reinforcing webs of the real KUAs.


The two updated KUA units, off the tracks.


KUA pair, ready to roll!

Some key dimensions


A slightly simplified construction technique was used to glue the central structure together.

(The cover is a press fit, with no glue bond to the base structure)



On the tracks


If my hand was a bit steadier, I'd change the "T" in KTA to a "U"......


To see one of these units in motion on YouTube click here

A Bit of fun:

I've added a super bright green LED within the front flask carrier. This can be connected to the adjacent Class 57 to produce some interesting? DCC controlled results.


 Simple circuit using a bridge rectifier to enable the plug and socket to work either way round.

The circuit glued in place under the flask cover. The green LED is the brightest one I could find at Maplin!     


Updates to the Escort Coaches:

1) Fitting a flashing rear light to the last escort coach:

All the photos and video clips I've seen show the escort coaches at the rear of the KUA flask trains. So I need to fit a flashing rear light here. Pick ups are fitted to the rear bogie wheels using phosphor bronze strips fixed at their centres to plastic blocks glued to the bogie underside. Wires are soldered to each strip and pass through holes in the bogie and coach floor, into the luggage compartment.  The circuit employs a full wave rectifier with smoothing capacitor, supplying a flashing LED via two series resistors. The flashing LED is used to provide pulsed electrical power to a small red chip LED embedded into a model of the standard UK flashing rear light. The 1k resistor in parallel with the chip LED ensures that during the "off" periods, the voltage across the chip LED is below the "on" forward volts drop and hence is too small to provide any illumination.  The rear light moulding comes as a spare part with the Bachmann FNA flask carriers. A 1.5mm hole is drilled through the lens position and a slot is filed in the rear to accommodate the chip LED.

Wheel contacts in place

Plenty of room for the inside circuitry


Circuit diagram


lamp moulding drilled, slotted & chip LED in place

Lamp installed on bottom coach bracket


The rear light is glued to the lower rear lamp bracket on the coach. The wires pass through small holes drilled adjacent to the lamp bracket, into the coach body, where they are soldered to the rest of the electrical hardware. The sides, bottom and top of the lamp moulding are first painted black to suppress light leakage. When dry, this is covered by white paint, and a transparent lens is applied in the LED hole, using "Glue 'n Glaze". When the lens is dry, red (translucent) water colour paint is applied to the lens front and a red rectangle is painted below the lens, to simulate the real Dorman lamps.


Lamp painted



2) Plating in the corridor ends at the outer ends of the escort coaches:

Photos show that the original corridor end doors of the escort coaches have been permanently plated over. The fill-in plate includes a small window, positioned just below the orange cant rail stripe.

The original Bachmann corridor parts were conveniently made as separate mouldings which could (with some difficulty) be removed.

A blanking plate was fabricated from a sheet of clear plastic, and glued in place using Glue 'n Glaze. The step at the base of the original Bachmann corridor moulding was sliced off and glued back in place.

The leading escort coach end before painting.


The window area was then masked with a rectangle of Tamiya masking tape, and a coat of Humbrol 15 (very dark blue gloss) was applied to the outside of the clear plastic blanking plate. Fox transfers orange cant rail strip was added just above the top of the window. The end of the coach was then masked and a thin coat of Humbrol enamel matt varnish was sprayed over the new parts. The masking was removed and the door step was touched in with matt black.

Leading escort coach with updated plated-in corridor aperture.

..........Next, the trailing coach!


The rear escort coach receives a plated-in end door too!


MOD train on the test track.




To see a You Tube video demonstration of the DRS M.O.D. Nuclear Flask Train click here


Supplier website links:


Hattons of Liverpool    The Dapol KTA container vehicles were purchased from this very reliable mail order company.
Rails of Sheffield    The Bachmann Class 57 locos were purchased from this equally reliable mail order company.
Model Rail Magazine    The KUA Mk2 escort coaches were part of a limited production run obtained from Model Rail Mag.
Bromsgrove Models    Good source of specialist parts for DCC projects (including the flashing LEDs used in the escort coach rear light).
Rapid Electronics    Good low cost mail order source for electronics components
Maplin    A good local source of basic electronics components including resistors and transistors


The photos of the model were taken on the kitchen worktop, mainly using a Canon Ixus 220 with a few complete train pics using the EOS7D at an f22 aperture to extend the area in focus.    


Click to move to Model Rail Index Page