For more than a century, rail power has fueled the rise of the modern world. Its mobilization foretold the reshaping of nations and the rise and fall of great empires. Its decisive role in the theatre of modern war often goes unrecognized. Behind the smoke and steel, great titans delivered armies to the front, shuttled supplies across continents, and carried wounded soldiers to safety. Evolving from a vulnerable target to an armoured weapon of war, how have trains become a hidden force during some of the world's pivotal conflicts? From the driving force behind the American Revolution, to the Royal Coach held hostage during the Danish-Prussian Wars. Which battle engines acted as a lifeline during the Great War? And why did some rail lines become targets for the Nazis? Cold War agreements transform trains into moving fortifications. How have trains carved vital pathways towards victory?