I think they are meant to act as permanent bases once reached their destination, not to be recovered anytime soon.

The logistics to keep such a thing alive would be obscene

I like to think it's a Fusion reactor powering those landcruisers. The game is set quite a few years in the future, so it's totally possible that it's fusion, though it could still be just a fission reactor.

I can tell Fundog's gonna be sweating to add an enemy variant of the Europan Titan for us to encounter in the game

When I first witnessed them, I was in total awe seeing a giant machine off in the distance start to slowly pull itself along the old highways, I love this game

I think they are supposed to be replacements for ships, which would make sense with the state of the world in the game and with the huge amounts of weapons they have it's very clear they also serve as mech hunters, because Kall has multiple dialogues where he clearly describes massive mechs especialy Iron Mother.
For the cradle questline, I think we are tapping into the city itself, because the Titan is sitting on the power source and from it. I think they are powered two ways, 1st somekind of nuclear reactor or something new and tapping directly into the powersource of the megacities like the one in Ashen Mesa

// multiple lines from Kall in his dialogues //
We tracked the Iron Mother by accident. Her tread marks were the size of buildings.
Saw a whole battalion she flattened. Looked like someone erased them with a rolling mountain.
Ash said she wasn’t a machine — she was a judgment.
Every time we got close, the radios screamed. Not interference. Screaming.
Dane thought she was heading toward Lost Angels. Mira said she was running from something worse.
I drove Low Bite between her tracks once. The ground trembled like it remembered fear.

We were crossing the Rustplain — that big, flat nothing north of Lost Angels where sound goes to die.
No dunes, no markers, no cover. Just heat haze and the sun laughing at us.
Halfway across, Mira stopped cold. Said she heard something under the sand.
Varro thought it was wind. Ash said it was probably our sanity finally cracking.
But then the plain… shifted. Like a giant exhaling.
(He leans forward.)
Dozens of old mech frames — buried Europan prototypes, long dead — started groaning under the heat.

We passed a mech carcass bigger than a stadium. Something had peeled it open like fruit.

The Iron Mother wasn’t hunting us.
She didn’t care we existed.
That was the worst part.
We followed her into an old industrial trench…
walls higher than towers.
Ash said it looked like a throat.
Varro told me to kill the engine.
Said he felt… watched
And Mira — she was whispering coordinates she’d never seen.
Dane got out first.
.....
Then the Iron Mother passed overhead.
Not crushing us.
Not killing us.
Just moving.
Her tread filled the trench like a sky doing its best impression of hell.
And the shadows?
They melted.
Like they’d only existed while she needed them to.

Vehicle that size has to be nuclear powered. Couldn't imagine what else you'd use

I can't get over the design of these Fatboy juniors.
Somehow mixing British 381s/japanese 356s taken straight off of Vanguard/Kongo with American Phalanx and Soviet AK-176 for self defence.
And then just a fuckload of missiles just for good measure.

it costs 10 billion dollars to drive this thing....for 10 seconds.

I never played this and probably never will, but how pleasant it is to learn this lore

Jawas have been really quiet since this dropped

id argue they aren't expendable its just that they are so absolutely colossal that if they break down there is no way to actually recover them.
they only way to recover one would be to disassemble it piece by piece  
with how large they are i have a feeling that not even having a second or third would allow you to even begin to move a stuck or severely damaged one
in fact it wouldn't surprise me if the instance where there are two of them is a result of that very attempt going wrong
the one that you show your able to go inside doesn't look like it was damaged from the outside which could hint at them having a protocol in place should they become immobilized
very likely its to detonate whatever power source the thing runs off of. my guess would be a nuclear reactor.
either that or they detonate their entire ammunition payload after packing it and anything of any actual true value in that massive blown out room you enter into.
if octo girls quest is anything to go off of they probably attempt the former before resorting to the latter

i dont think it actually does have ICBNMs those 8 pods on it are probably in actuality the cooling silos for a nuclear reactor
nuclear material is probably far to valuable at this stage to be for weapons
with how little of the stuff is probably left id be surprised if any of it is used outside of large scale power sources such as the titans.
i also dont realisticly see anything outside of a nuclear reactor being able to provide enough power to allow the titan to move anywhere near how fast it does.

as for the unidentified titan we see in the trailer all things considered its probably euruska
eurasia as we know is far more into the low orbit factory game. and have far more sleek and compact designs. its general stance/ posture also doesnt fit euasia
its hunched forward and even from the distance we see the top of it is seveerly rusted. its two forward guns are also clearly placed atleast in the cinimatic to look like eyes.
its oppressive  
another important detail that makes me think its euruska is that on the zoom in it looks cobbled together not to mention just under where the unknown unit square pops up to the bottom right there appears to be a head and torso
im not as convinced it looks like anything in the image afterwords

Smart, You can't sink a battleship that's intended to drive on land.

As far as an operational or strategic use for such a large unit... it kinda makes sense when you think about location. Such a massive unit would only be able to traverse relatively flat ground. It would be far too prone to tip over in mountainous or valley terrain. Since Europa is made up of NATO+South America, and the setting of Forever Winter's maps is near Arizona and New Mexico, then there are significant amounts of relatively flat land one can drive a giant vehicle over. Especially if the entire US is one giant megacity. The Interstate was explicitly designed to support the rapid movement of army units like troop convoys, tanks, and large cargo trucks. The whole country getting turned into a city for the sake of strategic dominance wouldn't let a little thing like NIMBYs prevent the construction of a transportation system for a WW3 military.

Supposedly, the Titan has many of the same superstructure and sensor layout as an Independence-class Littoral Combat Ship. That would indicate it's meant to be more of a tactical support unit. That said, if those VLS cells do hold ballistic nuclear missiles, it could be a replacement for the Minuteman-3 silos. Everything now being paved over and urbanized, and the concept of a ballistic missile silo was made in an era where accuracy was measured in blast radius, not yards. Much less drones. So a replacement would be "Mobile Silos". Land ships that are able to be repositioned anywhere in the megacity based on the threat. Which have nuclear warheads? The Navy will never confirm or deny, so the enemy has to treat every ship it sees like it's loaded to turn a country into irradiated ash.

This thing reminds me of several other vehicles I've seen in older sci-fi:  The Astra Militarum Leviathan and Capitol Imperialis mobile command fortresses from Warhammer 40,000, and the BOLO from Keith Laumer's 1960s novel series of that name.

Personally, in my humble opinion, I believe the unknown unit may be the "Big Green" unit seen in the artwork.
Mainly because it's with the Euruskan Toothy, but it could also very much be Eurasian.
But, I've been wrong before.

Maybe Titans were originally heavy landing/beach assault ships/AAV Assault Amphibious Vehicles ultra heavy variant. They landed on the beach and allowed to move heavy weapons platforms to secure objectives, on and beyondbeachfront. Clearly very naval centric design, with landing bay for marines and their heavy vehicles. LA is close to the Ocean, so maybe there was marines base near and they're using whatever they can? The question is if they could float... and is there any water propulsion tech visible. Overall the silhouette is very similar to the worlds largest assault/landing hovercraft- Zubr class hovercraft, at least that's my opinion, that they look similar.

One of the artillery systems on the titan is the russian AK-190, featuring a water-cooled barrel. That’s odd, because I would have expected something like that from Euruska.

"What is the Europan Titan?" Assault Destroyer Proud to Serve! Prepare for Land Approach! All it's missing is the Blackhole armor.
But beign serious I always like "landships" aesthetics they are always very cool. I think the Euroipan Titans also take inspiration from the Gundam franchise land battleships.
Edit: Rewatching the cinematic trailer I just noticed that the Ashem Mesa Titan appears to be moving backwards! At 3:33 you can see the Titan large quad missile pods.

3:00 the main guns on the Ratte looks to be comparable caliber on the several turrets the Titan has