This is a captured footage showing the massive railroad guns used by Germany during World War II. Some reports claim as many as 1200 troops were needed to operate the biggest railroad guns, that is a lot of manpower tied up.

The Second World War saw the final use of the railway gun, with the massive 80 cm (31 in) Schwerer Gustav gun, the largest artillery piece to be used in combat, deployed by Germany. 

Germany employed railway-mounted guns that were capable of firing across the English Channel between the areas around Dover and Calais. Germany also employed a number of 40 cm guns.

The rise of the aeroplane effectively ended the usefulness of the railway gun. Similar to battleships, they were massive, expensive, and, in the correct conditions, easily destroyed from the air.