Trotsky's "giant armoured personal train" was officially the 'train of the Predrevoyensoviet’ - the train of the Chairman of the Revolutionary Military Council. During the period of the civil war from 1918 to 1920, the train was the mobile home and base of operations for Leon Trotsky, in his role as War Commissar of the government of the Russian Socialist Federative Soviet Republic.
According to Rex Winsbury, writing in History Today, the train:
"... acquired an almost mystical significance for the commanders and
men of the Red Army, as it steamed into critical sectors of the
fluctuating front line, bringing trained officers and specialists,
fresh supplies, news of other sectors, and above all the reassuring
and sometimes terrifying presence of the War Commissar himself, who
harangued and inspired the slack - and sometimes had them shot."
Trotsky's War Train, History Today Volume 25 Issue 8 August 1975
or, as Trotsky wrote in his autobiography:
"during the most strenuous years of the revolution, my own personal life was bound up inseparably with the life of that train. The train, on the other hand, was inseparably bound up with the life of the Red Army. The train linked the front with the base, solved urgent problems on the spot, educated, appealed, supplied, rewarded and punished."
Trotsky: My Life, p411
It is, perhaps, worth noting however, that Jonathan Smele described Winsbury's article as:
"An insubstantial account of Trotsky's peripatetic leadership of the
Red army, drawn largely from his autobiography"