USC Marines History
The USC Marines first major engagement was the Asian-Christian War where they often landed on the shores of Asia. They landed almost 17 times on the Indonesian Islands all the times being repelled. They also engaged the Asians along-side the USC Army and a large portion died during Operation: Longsword.
The USC Marines during the time of peace often trained along-side the Army and even several attempts to have them integrated into the USC Army almost passed but were stopped by the Pope most of the time. They also had their 'swords dulled' during this time as they lost a lot of fighting prowess from the time of relaxation and relative peace.
The USC Marines during the Rebellion landed on countless worlds to allow the USC Army to take the planet. They often deployed into very hot landing zones and many were killed during the descent towards the planet itself from rebel artillery fire. They became famous for their daring raids on rebel worlds in which they were often suicide missions but they almost always achieved their goal.
Human-Covenant WarThe USC Marines during this time were almost utterly destroyed by the Covenant when they tried conventional tactics to land on planets. They soon adopted a Single Occupant Exo-atmospheric Insertion Vehicle for insertion. They carried only one marine but they were released en masse and as a result resulted in a much higher survival rate as they were extremely fast moving and when one was hit it killed only one not two dozen. They still had to contend with the highly superior Covenant arsenal and sometimes won pyrhic victories or more often getting totally destroyed after completion of their mission. After the alliance of the Sangheili and Mgalekgolo with Humans they only used SOEIV's for the spec-ops group the Orbital Drop Shock Troopers or ODST's. The insertion vehicle they used aft' that was the Phantom or Spirit for insertion.
Post Human-Covenant War
The USC Marines landed a squadron of ODST's in the final destruction of the Covenant at High Charity but was other wise not there.
Rebellion of New Quebec
The Rebellion of New Quebec was one of the major engagements of the Marines as they were the ones who almost solely established a beachhead on New Quebec. Other than that they did many ODST drops on the planet.