Military Training Pamphlet No.74 'Rafting and Bridging' Part IV, Bridge Classifications of Vehicles (other than 'A' vehicles and Mechanical Equipment laid out all the classifications and nomenclature for bridge markings in the British and Canadian Armys. I have yet to find a copy of this publication, but I did find a reference for changes made to markings for Tank Transporters, plus Bridge Classifications for operational vehicles of the Canadian Army for the D-Day period.
M.T.P. 74 Part IV - Bridge Classification of
Vehicles
(other than 'A' vehicles and Mechanical Equipment)
1. Sec.3. Delete Paras (e) to (l) inclusive and substitute:
"(f) Classification and marking fo towing and towed vehicles and transporters -
(i) Towing and towed vehicles, such as a tractor with its gun or a lorry/truck
with
its towed trailer, but excepting tank transporters, will be classified as
follows:
(1) The towing vehicle will be given a double classification as shown
in
A below. The upper number indicates the class of the complete
train
and the lower number the class of the towing vehicle alone.
A
B
C
(2) The trailer will also be given a double classification as in
B above.
The upper number indicates the increase in the load class of the normal
towing vehicle, which the loaded trailer will cause when in tow;
this number must be added to the lower number of the towing vehicle
to determine the classification of the complete train. The lower number
on the trailer is the classification of the trailer alone, in case it is
required to manouvre the trailer across a bridge by hand or winching.
(ii) Tank Transporters - Semi Trailers or Rigid Bodies
Tank transporters consisting of a towing vehicle and a semi-trailer
(such as the Transporter, Scammell, 30-ton, 6x4+8, Recovery) are
classified as a unit, and are given a double class sign as shown in
C above,
which is self explanitory and represents the complete transporter.
Note: The words "Train Laden" and "Train Unladen" may be painted
in
any convenient place.
(iii) Tank Transporters - detatchable trailers
In the case of those tank transporters which consist of a towing vehicle
and detatchable or independent trailer, the method of marking
will be
as follows:-
(1) The towing vehicle will have a double classification sign, the
upper
number indicating the class of the complete train and the lower
number the class of the towing vehicle alone. In addition, the
classification sign will will bear the name of the type of trailer which
it is designed to tow (See D and E below)
D
E
(2) The trailer will also have a double classification sign, the upper
number indicating the class of the independent trailer when laden,
and the lower number the class of the independent trailer when
unladen. The sign will also bear the name of the type of the trailer.
(See E and F below)
F G
Note: The words 'Trailer Laden' and 'Trailer
Unlaiden' may be painted in any
convenient place.
3. To determine the classification of the train empty, the bottom
number of the
trailer is added to the bottom number of the towing vehicle.
4. When a towing vehicle tows a loaded trailer of a type which does
not correspond
with the classification sign carried on the the towing vehicle, the laden
classification
of the trailer is added to the classification of the towing vehicle and
the train is
classified by the sum of those two figures.
5. The driver of the transporter will be charged with assessing the
combined load
class and will be held responsible that the vehicle does not cross a bridge
of a lower
class than the combined load classification.
(iv) Temporary Tow - For a vehicle
towing another in an emergency the classification of the
train will be the SUM of the individual classifications
of the separate vehicles. A class 9 vehicle
towing a similar vehicle will therefore have
a net classification of 18 and could cross any bridge
of Class 18 or above . This rule applies
particularly to R.A.F. trains.
(v) Transporters with varied loads - The Transporters in Appx C have been classified with the heaviest tanks they are designed to carry. Where a transporter is loaded with a lighter tank - as when an 18-ton tank is on a 30-ton tank transporter - a satisfactory classification is obtained by deducting from the maximum laden classification of the transporter the difference between the classification of the heavy tank for which it is designed and the classification of the lighter tank which is being carried.
This rule must NOT be applied in the opposite way - that is , if a transporter in an emergency is made to carry a tank heavier than that for which it is designed, teh addition of the difference between the classification of the "carried" and the '"design" tank to the laden class of the transporter, does NOT represent the new class.
(vi) In certain cases, such as REME Recovery units and Mechanical Equipment Units RE, where tractors may have to tow trailers of different load classes resulting in a different classification for the complete train, it will be necessary for the tractor to carry alternative discs to cover such combinations. In this case the disc must be suitably marked to enable it to be easily identified, and the driver (or NCO in charge of the detatchment) will be responsible for ensuring that the correct disc is fitted at the right time; the driver should be instructed as to the dangers of making mistakes .