This sequence of images illustrates Matilda II Infantry Tanks of the 1st Armoured Division being loaded onto what the wartime captions decribe as a "Special Rail Tank Conveyor" in July, 1940.
The design work on Matilda II began in 1936 and it was just coming into service at the outbreak of WW2.
It was the most heavily armoured western tank of the period, but its Achilles heel was the QF 2 pounder gun which, although perfectly adequate and the best in its class on its introduction, the fact that it could only fire AP rounds (no really effective HE rounds were available for it) proved to be a disadvantage as armoured warfare tactics and technology rapidly evolved as the war progressed.
Unfortunately, the diameter of its turret ring precluded "upgunning" with something bigger, due to the design parameters laid down in the mid 30s and linked to the need to transport it by rail, as seen here.
The flatcars were manufactured specifically to transport tanks.
The United Kingdom is a small country and its rail network although extensive ( remember...the locomotive and railways were invented here!) was on a rather smaller scale than in countries like the United States where the front half of a troop train could be in Oklahoma whilst the rest of it was still in Texas!
Anecdotally, when GIs began arriving in the UK they were usually transported from their ports of entry by train...which they found "amusing" as British rolling stock was so much smaller than what they were used to back home!
(IWM)
