My recollection is that they did use trains, at least during the worst parts of the war. (In terms of tanker losses & shortages.) But an oil tanker is vastly

My recollection is that they did use trains, at least during the worst parts of the war. (In terms of tanker losses & shortages.) But an oil tanker is vastly more efficient than train full of tanker cars. And the supplies of tanker cars, rail lines, locomotives, & etc. were all pretty constrained.