A steam engine was used for more then moving machinery.

Robert Fulton used it to build the first steam boat in 1807.

So because most industrial cities were built near lakes, rivers, and canals, the steamboat became one of the best ways to transport manufactured goods like coal, and iron to other cities.

In WWII a lot of these vehicles have been used for war.

All the land, sea, and air vehicles were made as units instead.