Appearance in Galaxy Railways
Big One is painted in the typical livery given to its basis. The number on its tender is the number 001, a shorter version of its official number, G8001. In the sequel series, Galaxy Railways: Eternal Divergence, it gains smoke deflectors and a larger cowcatcher (which looks more like a snowplow truck). Big One's wheel arrangement also changed; in the sequel series it is a 6-8-8-4 instead of a 4-8-8-4. It was based on the Union Pacific 4000 Class 4-8-8-4 Big Boy Articulated Steam Locomotives by the SDF. Big One appeared in lots of episodes but was destroyed in Episode 1 of Season 1 but was later rebuilt and would later receive upgrades in Season 2.

Basis of the SDF Big One Locomotive
Big One is based on the Union Pacific's 4000 class of 4-8-8-4s, commonly called "Big Boys," albeit with an extra headlight in place of its bell and the Sirius Platoon insignia bolted to where the Union Pacific logo would be on the prototype. Although a normal Big Boy weighs over 1 million pounds, due to the Galaxy Railways not having steam engines that constantly needs people to operate it, this greatly reduces Big One's weight which would be in the 300,000-600,000 pound range instead of the normal 1 million. This doesn't keep the engine safe from wheel slip as seen in both season 1 and 2. This also means Big One's coaches are heavier than a normal coach.

Weaponry of the Big One Locomotive
Like all SDF locomotives, Big One has a cannon mounted in its undercarriage (season 2 only). Big One's coaches are specially built for medical attention, rescue, and feature cars with rotating turrets and fast-firing "space vulcan" rotary energy machine guns.