Railway troops built and operated hundreds and hundreds of miles of narrow-, extra-narrow- and ultra-narrow-gauge railways behind and right up to the Front positions, especially to Artillery emplacements. They were utterly necessary and it was a risky business, being that Fritz knew how important they were and regularly made targets of the railways.
A 6-inch Howitzer Mark VIII, for example, had 2 weights of shell: the lightweight shell at a mere 100 pounds, the standard heavy shell at 122 pounds. That is the weight of the Projectile, per shot, and does not include propellant or fuse. Half a dozen guns firing a round each every 5 minutes would require more than 100 TONS of shell per day....... plus propellant and fuses. And Howitzers are relatively short-range guns........ but they must be fed.
And so the Trench Railways came into being: steam railroads to carry the immense quantities of warlike stores to where they could be used. They were tiny railroads with tiny locomotives, some as small as 8-inch gauge although 12-inch and 18-inch were more commonly used..... where they could be used..... and they carried everything. A single crate of .303 ammunition weighed 74 pounds but held only 1248 rounds: enough for half a platoon at normal scale, enough for a small section at frontline allowance; 1500 crates to ONE Division for a weight penalty of 55.5 tons, plus another 3 tons of Chargers. Canada alone had 4 Divisions at the Front.
The War would have dragged on until the 1950s (see Bairnsfather's immortal cartoon) if it had not been for the Railway Battalions.
And today they are forgotten.
Hoist one for Great-Grandpa!