Thomas is -strictly speaking -a "side tank engine" -a steam locomotive that has tanks arranged on either side of the boiler.

严格地讲，这个叫做托马斯的火车头是一个两边都装有水和燃料罐的蒸汽火车。

youdao

In 1804, the Englishman successfully set the steam engine the running vehicle, and thus the first set of steam locomotive appeared in the world.

1804年，英国人成功地将蒸汽机安置在运行的车辆上，从此，世界上有了第一台蒸汽机车。

youdao

They travelled in coaches pulled by an 1898-built steam engine, known as Met Locomotive No 1.

BBC: London

The locomotive is being refitted with vacuum brakes to enable it to tow the steam engine and carriages.

BBC: Steam train to return to London Underground