So the Marine Corps was tiny at the outbreak of the Civil War. The entire force numbered 1,758 men and 63 officers. There was minimal desertion from the enlisted ranks, but 20 officers resigned their commissions. The authorized side of the Marines would be increased, but even by the end of the war it was at 3,882, which obviously was very tiny. Compared to the Army, the Marines had a severe disadvantage when it came to recruitment. There was no enlistment bounty to entice a recruit, and no enlistment contracts for a short term such as available with the Army, so even maintaining that small number was not easy and the Corps remained below its authorized strength for much of the war.

For the most part, the Marines role was restricted to Naval installations and shipboard service, and action that they saw was through involvement in boarding parties and shore assaults. We'll return to this, but first I'll briefly address the two principle non-naval engagements that saw the Corps in action, plus a bonus which, technically, predates the war. Harper's Ferry was the site of John Brown's brief attempt to incite a slave rebellion, and as part of the force dispatched to nip the insurgency in the bud were 87 Marines stationed at DC's Navy Yard, placed on a train with two 12 pounders and sped over to bolster the militiamen and soldiers. Under the overall command of a certain Col. Robert E. Lee, the Marines would lead the assault on the arsenal building held by Brown's men, with one of their number cut down in the fight.

Once the war began, they would see involvement in only one major land battle. The battalion of 350 or so Marines who made up the Navy Yard garrison were marched into Virginia along with the Army as they headed towards the first significant clash of the war, at Manassas. Barely a handful of their number had anything one would term "experience", most of them having been recruited within only the past few months and in many cases essentially untrained. The Marine detachment experienced... mixed result. They acquitted themselves bravely enough on the battlefield, standing up to several instances of galling fire with only a few, temporary waverings, but they hardly distinguished themselves either. Some did, for a time, serve are part of the rear-guard when the Union forces began to quit the field, but many others joined the rest of the rout, and 70 or so were arrested by the Army provosts. On top of that, they suffered 8 killed, 16 missing, 16 wounded.

Later on, to coincide with Sherman's march towards Savannah, the South Atlantic Blockading Squadron was created with 157 Marines and roughly 350 sailors, and moved by boat up river for attacks on the Charleston and Savannah Railroad, operating in conjunction with a Division of the Army. In the field with the Army for roughly a month, there were several engagements with the Confederates, and overall they enjoyed little success with regards to their intended mission. They were withdrawn once Sherman took Savannah.

Now, while field service was uncommon, through the war they would serve in their principal form - ship detachments and naval infantry. I will not go through every incident, but I will mention a few highlights. For a few examples of service at sea, I'll start with the Judah raid. One of the most heralded actions, it occurred in September, 1861, with a detachment of Marines, augmented by sailors, departing under cover of darkness from the USS Colorado to board the Judah, which was a suspected privateer based out of Pensacola. The raiders successfully set the ship afire, and also destroyed the Columbiad gun on shore defending the naval yard.

Another notable action involved the Marines of the USS Galena, an ironclad sent up the James river as part of a small flotilla on May 15, 1862. Stopped by the Confederate defenses at Drewry's Bluff, the ships were taking heavy fire, and led by Corporal Mackie, the Marine detachment stepped up to man the ship's Parrot Rifle when its guncrew were taken out. Of interesting note, the shore defenses were manned by members of the very small, and mostly unused, Confederate Marine Corps. Mackie would become the first Marine to earn the Medal of Honor for his action.

As for naval infantry, I'll mention one notable incident. The attack on Fort Fisher on Jan. 15, 1865 was not just Marines, being in fact the largest amphibious action of the war. Part of a two-pronged assault, 400 Marines and 1,600 sailors were landed to assault the fort from sea, while the Army (and 180 more Marines) brought a separate force, landed further away, to assault the land approach. The naval assault became mired down, in part due to delays by the Army's half of the operation. Unable to capitalize on the breach they made in the wall, the Marines and sailors hugged the sand and did their best, and while they were unable to take the fort themselves, they did their part, serving, if nothing else, as a diversionary assault for the eventually successful landward assault. There would be a few minor exchanges of fire later, but that was it for significant battles by the Corps in the Civil War.

Mostly sourced from reading "American Civil War Marines 1861-65" by Ron Field

As a follow-up, I know a Marine battalion was present at First Bull Run, but as far as I know the Marines didn't partake in any battles following that. Why were they there, and why did they not fight in battles afterward (or did they)?