The one advantage for the Marines is geography.
They will know places the Romans don't know about.
The one advantage for the Marines is geography.
They will know places the Romans don't know about.
???
Nitrocellulose (guncotton) is easier to produce than black powder. It's nitric acid + cotton. Nitiric acid can be easily made from ammonia vapor passed over a platinum/rhodium catalyst. Some fuming sulphiric acid to help the saturation process. Ether and ethanol for extrusion that is recovered in drying. Ta-da. Much better than scraping cesspits for KNO3.
Hell, you could make double-base powder by adding some nitro-glycerin. Nitric acid + gycerin (a byproduct of soap making).
The biggest issues would be quantity and quality. Not enough and what was available would not work properly in weapons as stabilizers would be unavailable.
Primers are more difficult as they are made with azides. You could go old school with fulminates and perchlorates. But they are fouling and corrosive and would probably not work well (or at all) in modern weapons.
As mentioned before, the Marines would more than likely annihilate the first Roman unit that goes against it. And there is a possibility that they will be able to survive and create a living, or the Romans may be impressed with them enough to have them join the Empire.
However, if the downfall of the Roman Empire is a goal, then things might be a tad challenging, superior firepower or no.
First off, if we are going along the Cortez and Pizzaro arguments, we are to assume that they are now cut-off from any supply source.
Alien disease would not be a benefit for the Marines, but would likely in fact be a great hindrance; how much is a that generational immunity worth after a millennium or so when you are being expose to the original source + other stuff.
Also, the Romans are potentially be a lot more pragmatic in the way they view this alien technology, as evident in the way they have reacted when coming against new technologies that their enemies used; I highly doubt that the "sufficiently-advanced tech" law would be in play here, even with gunpowder.
But the main obstacle would be the sheer scale of the Roman Empire. Let's say that they arrived during Hadrian's reign. Of course, if we dropped them right by Rome, there is a good chance that downfall may occur; though you would then deal with the likely splinter empires that would form from that. But there is no fun in that. Instead, have them start at the banks of the Euphrates, the shores of Gibraltar, of the forests of Brittania. With that, there is a bit more of a challenge. Soon, without that supply source, any heavy machinery/vehicle would be rendered obsolete. Also, Roman military would likely not be the only adversary the Marines would face. Tribes hostile to everyone, brigands, more disease, and more.
The Romans probably do recognize the concept of running out of supplies, especially if they manage to capture some equipment. So who is to say they don't simply take a ton of slaves, plebeians, POWs, etc and press-gang them into serving as one big zerg rush (entice them with citizenship upon survival). After that wearing-down, then their main force can be utilized.
With all of that, conquering the Roman Empire isn't going to be the curb-stomp battle that is envision. The main way I see this occurring is the presence of allies and backers. Make deals with tribes and dissatisfied provinces (especially those who have been recently conquered or put down). Possibly appeal to the big players such as the Parthians/Sassanids. With each consecutive victory brings the possibility of more allies wishing destruction of Rome.
Though that also begs the question if the Marine presence is going to make Rome reassess its foreign relations. Possible greater alliances/peace treaties and contingencies formed against this new threat.
I'd generally lean towards the USMC in this sort of thing - defeat a couple of legions, take Rome, and call it good. But...
What if the USMC had to face Titus Pullo?
I can imagine that Rome could fall eventually just from the spread of modern strains of influenza and various infectious disease or vice versa, with the Marines getting afflicted with diseases from the past. I admit to not knowing much about military tactics, strategy, and logistics, but would it be a good idea to hunker down over the long term to conserve fuel and ammo, take the high ground, and use armored vehicles to just crush the poor Roman blokes in tight formation? Not like the Romans have anything that can take out an armored vehicle.
Living off the land would be a problem, and eventually ammo would run out. But not before well aimed grenades, mortars, or explosive charges take out huge swathes of Romans in conveniently tight formation.
Like Ira siad the Romans will adapt to new tech. The Marines are doomed
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