As seen within nearly every episode of the Galaxy Railways the main and only locomotive that is headed by the Sirius Platoon is labeled as, "Big One".
Presumably known as the "Pride" of the Space Defense Force (SDF), the engine has a record for being the most "reliable" of the fleet.
The locomotive itself is based on the Union Pacific Big Boy locomotives that were built by the American Locomotive Co. of Schenectady, New York, between 1941 and 1944, and are some of the largest and most powerful steam locomotives ever built.
Much like its real-life counterpart, Big One sports a 4-8-8-4 wheel arrangement...a four-wheel guiding truck for stability entering curves, two sets of eight driving wheels, and a four-wheel pilot truck to support the massive "firebox". On the box artwork of the OVA The Letter From The Abandoned Planet Big One appears to have a 6-wheel lead truck, making Big One a 6-8-8-4.
Upon its cowcatcher railing, it sported the emblem of the Space Defense Force ( Where the usual UP logo would be IRL. ). It also sported two headlights, one near the cowcatcher railing, and another just where the bell would be, before the large, double smokestack.
Another would be the numbered plaque labeled "G8001" upon the loco's boiler face, instead of upon the head of such. A shorter version, labeled "001" is also printed across the locomotive's large tender.
The final change were the whistle, it now has a bit of a deeper/darker tone to it than upon the real life Big Boy.
In Season 2, Big One gains Smoke Deflectors, and a more streamlined cowcatcher, and has also been modified with a 6 axle leading truck like in Letter From The Abandoned Planet, making it a 6-8-8-4.
Being owned by the Space Defense Force, like many other locos, Big One is retrofitted with some of the era's peak technology, advanced to the point to where even science cannot explain it in full detail.
"Flight" - Thanks to the modern, not to mention somewhat "Alien" technology of such a future, all trains that run upon the tracks of the Galaxy Railways are bestowed with the ability of "flight", or "Interstellar Travel" as many would call it. In actuality, the vehicles do not truly "fly", and are more so held in place by the constant forces of the magnetic barriers which carry them up and out into places beyond.
Naturally, the structural integrity of the consist, along with it many components must be within peak conditions, in order to preserve the safety of the many passengers who ride the Railways each and every day.
"Magnetic Barriers" - Such are considered as necessary within the depths of space, as it is practically a vacuum. Without it, trains would not be able to land, or even take off.
They are also utilized for protection against natural causes, say a swarm of meteors, space pirates & whatnot.
Warp Drive Coupling Unit" - Much like Imperial Cruisers and Warships in Star Wars, of even the vessels in Star Trek, all Galaxy Railways trains are equipped with a "Warp Drive" system. This allows for near-if-not-already-exceeding lightspeed travel, which is quite convenient, as the Railways stretch across an immense portion of the galaxy, if not already all of it.
Main Battery Car" - The strange gray-ish looking car within the middle of the consist is actually called the "Main Battery". This is where the power for the weapons go to. Upon the vehicle, there are nine large turrets upon the sides and top of such. They are very maneuverable, and can swivel 180 - 360 degrees as a whole, or 45 degrees as singles.
When in use, magnetic power is sent towards such, and converted into a physical / visible source. Which is then utilized against the enemy.
Their power were yet to be challenged within the series, as thanks to the "Cosmo Matrix" given by the plant-like extraterrestrial "Lilthel," at full power, within Season One alone. However, using the Cosmo Matrix causes the weapons and other systems to become overloaded, which can lead to breakdowns or loss of power to some or all systems. This is fixed in Season 2.
Off-Track Mode" - In addition, it has a feature known as "Off-Track Mode", which allows the locomotive to travel to areas outside of "track limits", where no regular loco in its time could trespass, as it would normally be impossible for a train to even move.
Within such a state, the train can be used to avoid enemy fire with particular ease, or for "planet hopping" in areas outside of the Galaxy Railways near universal range.
Independent Talking Devices - It is seen in some episodes when Big One is in another universe, that Big One is definitely alive, and can talk. More proof to this is linked in episode 22 when Big One chooses to take Frell with them, when Yuuki says that she should stay behind again.
Big One usually pulls a consist of nine coaches within its tow (( Not counting the Main Battery car)), each withholding some sort of particular value. The coaches are based off old Japanese passenger coaches in design.
The first three mainly serve as a medical room for the crew, a lounge, and refuge for rescued passengers.
The fourth, and fifth house the miniature energy turrets, which serve for deterring enemy fighters (( AKA, mini-cruisers, War-Jets, etc. )) from attempting the destroy the consist in one go. However, there is only so much. that they can handle within their range.
Coaches six through eight house three all-around fighter aircraft. Much like modern day aircraft, they can seat up to two people, and can operate within almost any climate, whether it be within the cold depths of space and whatnot.
The ninth coach s basically the same as coaches 1-3, except equipped with a rear observation deck.