why did the U.S. Marines (an amphibious force) fight in Afghanistan (a landlocked country)?

Marine here. Though amphibious operations are our bread and butter, they’re not the entirety of what we as a force are capable of doing. Every branch has something they can do better than anyone else, but it doesn’t mean that’s ALL they do. Hell, even the Army can conduct operations on water.

We were at war in Afghanistan, and the Marines are a piece of our warfighting capacity. Afghanistan is a big country with a lot of people, and conducting an occupation and counterinsurgency operation at a certain scale takes as much as we can provide, especially with a concurrent war in Iraq and American forces already stretched relatively thin at times with global commitments.

You don’t neglect to employ an entire military branch of almost 200,000 personnel just because the mission doesn’t completely line up with conventional wisdom on how that branch is intended to operate. You make it work.

So generally the US marines are more like an Expeditionary force or a rapid deployment force more than just amphibious fighting force. So before modern standing armies were a thing, historically you needed an experienced field army to perform smaller military operations and to be the first fighting force for a larger conflict. They do the fighting while the rest of the military drafts forces and scales up. Similar principle applies.

I’m not too familiar with Marine policies specifically in the 90s,2000s, and 10s, but more or less they do operate as a smaller but self contained full military. They had jets (typically air force or navy), ships (typically navy), infantry and attack choppers and tanks (typically army) and can work in a more uniform command structure with supply and transport from the Navy. They only really lacked submarines and dedicated satellites.

Now the modern marines are reforming to be a more lighter and faster assault force. As a result, they disbanded their armored units and got rid of their Abrams due to logistics difficulties of moving such a heavy piece of hardware. The military in general is in the midst of a massive overhaul with new guns, new planes, new tactics, new everything. This is especially true for the the Army, while the Marines have to get things approved out of the Navy budget, more or less.

Essentially the USMC are intended to be a rapidly deployable “strike” force that can take a wide variety of objective types. They can operate completely on their own (they have their own Cavalry* (attack helos) that can keep pace with a quick moving ground force, boats, and their own mini Air Force to ensure they have their own air support that doesn’t need to be borrowed from another service branch.

The catch…..they can do this, but only for a limited time. Think 30-90 days before they run out of supplies and will begin to need external support (calm down crayon eaters, this is Spiegami).

The difference ….. the Army is intended to be a long hold massive war type force that plans to stay around a long time.

Why the USMC in Afghanistan? They’re that good, and they were available – so why not. Jokes aside, I’m guessing that once they showed up, there was a constant need for them to stick around and do what they do. In hindsight, that thater was such a quagmire they never would’ve run out of stuff to do.

TLDR: They specialize in a wide variety of geographical and operational environments. They have much more flexibility in how they operate by design.

To simplify the other stated points, which cover the reasons pretty well: The Marines functionally are a 2nd Army. AKA they blow shit up and hold territory, the primary use cases for any given military force. The USMC is designed for expeditionary warfare, a mission set which evolved out of their amphibious/naval warfare roots.

At any given time, some Marines are floating about on Navy ships ready for rapid deployment. The ships sail to the nearest coast of wherever they feel like invading/humanitarian aiding, the expeditionary part. The Marines disembark (the amphibious part) and do their thing for up to 15 days, by which point they are hopefully not dead and are either finished or reinforced.

When not on the boats, Marine units function very much the same as an equivalent Army unit and so are largely interchangeable as far as the big picture Generals are concerned.

For historical and bureaucratic reasons, the United States Marine Corps evolved from its traditional role as shipboard naval infantry into the Department of the Navy’s Army, complete with armor, field artillery, mechanized fighting vehicles, and rotary and fixed-wing aviation. A significant portion of their combat support and combat service support functions are still provided by the Navy since originally they were never intended as a separate independent branch; for example, famously the Marines do not have their own medics or doctors. Further they have some odd blind spots in their force structure: they do not have mechanized/motorized cavalry, and consequently lack certain scouting and reconnaissance capabilities that equivalent army formations have. But nevertheless, despite this rather strange historical evolution, the Marines more or less have the same land war fighting capability as the Army, and are perfectly capable of fighting deep inland, even in landlocked countries. During the GWOT, there was tremendous political pressure not to expand the size of the military and most certainly not to resort to a draft. As a result, the us military was stretched very thin fighting two wars at once, and it was all hands on deck for the better part of a decade, where every Army, Marine, National Guard, and Reserve unit was either deployed, just coming back from deployment, or preparing for the next deployment. As a result there wasn’t the capacity to have the Marines sit Afghanistan out just because the country is land locked, which is not at all a limitation for them to fight effectively.