RNAS Armoured Train

This is a British Armoured Train design for Shadowless, based on real life armoured trains operated by the RNAS (Royal Naval Air Service, the air arm of the Royal Navy) in Belgium during the early part of WW1.
Most of the cars are either copies of real life examples from the 1890s or based upon them and modified as the story requires.
One such example is the "Ordnance BL 20 inch Railway Howitzer", which is an enlarged mash-up of the real life 1918 "Ordnance BL 18 inch howitzer on truck, railway" and the 1915 "Ordnance BL 12 inch Gun Mk IX".

Since this drawing is primarily meant as reference for the comic, I only drew the different type of cars and not the way they fit into the completed convoy. In operation, the actual car order would be: 1_2_3_4_8_9_6_5_5g_5g_10_7, where "5g" is a "gunpowder van", similar to the general goods van but with the sides made out of steel plate instead of wood (for obvious reasons).

EDIT, 22.03.17: I'm slightly revising the weight calculations and the composition of the convoy, because it appears that, while they were "quick and dirty", they were "too dirty" - for one, I misread the weight of the locomotive, which did NOT include the tender. Also, I had the barrel and breech at 85 tons and the whole howitzer at 115 because I was extrapolating from the 18 inch gun I used as inspiration, but all actuality the barrel and breech alone would weigh in 115 tons and the whole piece should be more like 215.
So here are the revised numbers:

The "Claud Hamilton" class (LNER Class D14 or GER S46) 4-4-0 engine has a tractive effort of 76,040 N (17,095 lbf, if you prefer imperial measurements) and accounts talk of a Claud Hamilton setting a speed record pulling a 400t train 130.2 miles (129.5km) in 157 min 24 sec, which means an average speed of 49.63 mph (79.87 km/h).
Another source gives the typical train freight train composition for this era was 42 fully laden 10-ton two axle cars, totalling 420t.

Assuming the larger weight for a slight decrease in speed and adding the weight of the locomotive and tender (52 and 39 t respectively) we get an average convoy weight this locomotive could pull "comfortably" of 514 gross tons (so including the weight of the train itself, or "tare").

As can be inferred from the above, the weight of the locomotive itself is 52 tons normal and 105 after armouring with 8 -12 mm plate, the fully laden tender weighs in 39 tons normal and 45 armoured (not much armouring on the tender, for obvious reasons) while the weight of the armoured cars is 22 for the machine-gun car, 30 tons for the artillery cars and 12 for the two-axle command car.  The howitzer itself is 215 tons, of which 115 are in the barrel and breech itself.  The rest of the train cars are between 8 and 10t each because they are standard freight cars while the front wagon only weighs in 6.4 tons, because it's only loaded with some sandbags and a machine-gun.

Putting it all together (according to the train composition given in the description) we get a total train weight of 513.4 gross tons, which, as can be seen from the above figures, is exactly within the ballpark for the afore mentioned locomotive.