What is the role of the U.S. Marines under contemporary joint warfare doctrine?

Question

Is the U.S. Marine Corps, as a separate branch, largely a historical artifact, or does it fulfill a distinct purpose within the context of modern joint warfare doctrine?

Please note, this is not questioning the value or contribution of the Marines in either historical or current conflict. This question will undoubtedly irk some people, but I'm asking in earnest whether a group of strategists in a developed nation who were in 2023 deciding how to organize a military would seriously consider something like a Marine Corps as a distinct branch, or whether it is a historical artifact based on pre-20th century strategy and technology.

The background for this question is that in a conversation with a foreign friend, it came up that U.S. Marines are sometimes called "jarheads" for some reason I did not know. The foreign friend said, "Maybe it is because of the shape of old diving helmets." Confused, I asked why that would be an influence. And of course, it is because the name "Marine" made her assume that U.S. Marines operate exclusively in, well, marine environments. When I thought about it, the original purpose of the Marine Corps was

1. Seizure or defense of advanced naval bases and other land operations to support naval campaigns;
2. Development of tactics, technique, and equipment used by amphibious landing forces in coordination with the Army and Air Force; and
3. Such other duties as the President or Department of Defense may direct.

#1 Is still relevant, but it seems to largely assume that branches carry out independent campaigns and operations. That isn't really true anymore, as most campaigns are now joint efforts. Every branch now supports every other branch, so this niche doesn't seem to exist anymore.

#2 Is essentially obsolete, as troopships are all but obsolete in modern militaries. "Amphibious landing forces" have been more or less replaced by airlift transport and paratroopers. Even 80 years ago in the most renowned beachfront battle in U.S. history when troopships were still used, the beaches were stormed by Soldiers, not Marines, were they not?

#3 Is not specific and could be said of any conceivable uniformed service.

So again, does the U.S. Marine Corps still fulfill a distinct role given the dominance of joint warfare, or are they mainly a separate branch for historical reasons?

EDIT: The original title of this question was "What is the role of the U.S. Marines under a contemporary combined arms approach?" Based on comments and answers, I've revised the title and question to more appropriately use the term joint warfare rather than combined arms.

Answer 1

Marines define themselves as a medium-weight, expeditionary, high-readiness force, as well as the amphibious force.

That is, the Marines are slower to deploy than he Airborne, but they pack more punch. They are faster to deploy than the Army heavy forces, but they pack less punch (especially when it comes to things like Corps-level assets). One might argue that the Army SBCT aims for the same niche.

The Marines train and organize on the assumption a battalion-sized force might control their own artillery and aviation. This differs from the Army, where such assets would be pooled at a higher level -- possibly more efficient, but also more cumbersome to get deployed.

A cynic might also observe that the US is big enough to afford a redundant branch of the Army/Air Force, just as they can afford a second Navy in the Coast Guard. Other countries do not.

Answer 2

Combined arms is an approach to warfare that seeks to integrate different combat arms of a military to achieve mutually complementary effects—for example, using infantry and armour in an urban environment in which each supports the other)

(Source)

The notion of combined arms is of cooperation of different kinds of military units, like infantry, armor, air power, and perhaps fire support from ships off shore, towards a single task or mission.

The Marine Corps has in recent history been the model of a service in which combined arms are deployed within the single service.

The Marine Corps has integrated infantry, armored forces, and both helicopters and fixed wing fighter aircraft, often with sea based support, in the same military service, rather than divided between separate military forces.

In contrast, for example, the U.S. Army receives its fixed wing fighter aircraft air support from the U.S. Air Force. Similarly, the U.S. Army generally relies upon the U.S. Air Force and U.S. Navy to be deployed to the theater of combat.

Within the U.S. Army, combined arms refers to the cooperation of infantry, armored vehicles, and sometimes armed helicopters, working together in a mission.

Fun fact: despite the fact that the U.S. Marine Corps sees amphibious assault as one of its core missions, the most famous amphibious assault in history, the D-Day Invasions, was a joint Army-Navy operation.

Answer 3

Other answers have already discussed the continued relevance of the US Marine Corps in contemporary warfare; however, the answer to the question in your first paragraph ("is the USMC as a separate service a historical artifact?") is obviously yes. If you were designing a military command structure from scratch, there is just no way you would decide to take the "medium weight expeditionary force" (thanks to poster o.m. for this description of the USMC's mission), and only this force, and turn it into a separate service.

In fact, if you were starting from scratch, it is debatable whether you would have separate services with their own command structures at all. Having administratively separate services, like the Army, Navy, Air Force, Marines, and now Space Force in the US, creates waste, inefficiency, and duplication of effort. Service commanders compete for turf, and then build redundant capabilities internally to avoid having to rely on support from other services. The most egregious example of the inefficiency of inter-service rivalry is the feud during the Second World War between Admiral Chester Nimitz and General Douglas MacArthur, which resulted in the Pacific being effectively partitioned into areas "owned" by the two commanders. However, the tension is always present to some degree.

One real-world example of military leaders recognizing the inefficiency of separate services is the armed forces of Canada, which in 1968 were unified to form the Canadian Armed Forces. Unfortunately, I was not able to find any analysis of whether the consolidation achieved the expected improvements in efficiency and effectiveness. However, it is significant that the incremental rollbacks of the unification in recent years have always been supported by arguments appealing to tradition rather than to concerns about operational effectiveness.

Answer 4

Look to o.m.'s answer for a complement, so I don't need to repeat it.

I will add some extra considerations however:

First, all militaries are extremely slow to evolve, doubly so when it comes to their branches, which typically see intense rivalry to preserve prestige and funding. The US is not exception. Even if what you said was correct, one could expect the Marines to tick on for a looong time.

Second, "Marines" makes it sound like we are talking about a proper noun. They are not, really, they are a common noun. The notion of shipboard infantry spans millennia. In French for example, we have "fusiliers marins", marine riflemen. Many countries will have similar forces. True, most countries don't have a whole Corps of them, but then again most countries have nearby continental neighbors to worry about. So their ground forces aren't, primarily, organized around distant force projection. The US's ground forces are likely to be operating way outside of US territory however. And the US is spendthrift, defense-wise.

Third, airborne as a solution sounds neat. Except for the airborne armor bit. As the poor sad Russian VDV has found out in Ukraine, you can have light IFVs. Or well-armored IFVs. Not both.

. For example, elite but relatively lightly equipped units (such as VDV, spetsnaz, and reconnaissance units) conducted operations they were not trained for or equipped to conduct, such as advancing into urban areas, where they appeared to suffer heavy casualties due to the lack of heavy armored support.

Don't let 50 years of mostly counter insurgency US warfare fool you: fighting a peer opponent requires a different, heavier, mix of tools than keeping the peace in a poor country.

Fourth, to some extent the Corps is aware of the issue. Combined with the pivot to the Pacific theory and the US desire to contain China, the Corps is currently conjuring up a new doctrine - Force Design 2030 (subject to considerable internal disputes within the Corps):

• drop heavy tanks
• switch to lighter forces armed with drones and long range land-to-ship missiles
• prepare to disseminate smaller, stealthier, Marine groups throughout the First Island Chain and ambush Chinese Navy ships from land, using those long range missiles.

wikipedia

Basically, pull a bunch of Moskvas on the Chinese Navy.

I don't know how well that would work out in practice. It sounds gimmicky, but does have the theoretical potential to be an awesome asymmetric, David-vs-Goliath approach.

I do know this is not a mission that would be suitable for standard US Army troops, since it has a much more naval component to it. Both in the operating environment, and in the specialized heavy weapon mix that is required.