Luxembourg was a founding member of the United Nations, being signatory to the original 1942 declaration, so certainly felt some level of obligation to participate in the United Nations military mission to Korea, although pressure from NATO should also be understood as a factor. Although Korea was obviously not covered by the treaty, there was a drive to increase the military abilities of the smaller member nations, and Korea presented a strong opportunity for that to focus on, resulting in most nations contributing to the UN military mission also being NATO countries, or closely aligned. However, being a very tiny country, with an equally tiny military - even with universal conscription - they weren't able to send over a contingent capable of anything approaching self-sufficiency, so their small contingent (smallest of any country in Korea) was folded into the ~900 man Belgian military contribution to the conflict, something not without precedence as Luxembourgian soldiers has been similarly attached during World War II, as part of the Free Belgian forces. As such, the Luxembourgers formed 1st Platoon, A Co. of a joint Belgian-Luxembourg Battalion, which was in turn attached to the US 3rd Division.

Although originally outfitted with British surplus, being within the US military umbrella they were reequipped with US hardware. It is hard to say whether they made a difference as that is a tough thing to evaluate, but we can say that they did their part, seeing action in a number of engagements, both big and small, and earning multiple US Presidential Unit Citations, the first on Sept. 6, 1951, reading the following

By decision of the President concurrent with the dispositions of the execution order 9396 (Sec. I, War Department Bulletin 22, 1943) etc. ... , the following unit is mentioned on the daily order as a public testimonial of deserved honor and distinction.

Citation : The Belgian battalion with the Luxemburg detachment of the UN Forces in Korea is mentioned for exceptional execution of its missions and for its remarkable heroism in its actions against the enemy on the Imjin, near Hantangang, Korea during the period from 20 till 26 April 1951.

The Belgian battalion with the Luxemburg detachment, one of the smallest units of the UNO in Korea, has inflicted thirty-fold losses on the enemy compared to its own, due to its aggressive and courageous actions against the Communist Chinese. During this period considerable enemy forces, supported by fire by machine guns, mortars and artillery, repeatedly and heavily attacked the positions held by the battalion but, Belgians and Luxembourgers have continuously and bravely repulsed these fanatic attacks by inflicting heavy losses to the enemy forces. When the Chinese troops had succeeded in occupying positions endangering the liaison with the allied neighboring units, The Belgian battalion with the Luxembourg detachment launched furious counter-attacks with the bayonet. The enemy, surprised by the tenacity of these attacks became disorganised and withdrew in disorder. Finally, the Belgian-Luxembourg battalion withdrew by order of higher authority, evacuated its wounded, was resupplied and requested to be put back in the line.

Having arrived at the frontline again, numerous enemy infantry and cavalry units were observed heading south. When the enemy was sufficiently close, the Belgian-Luxembourg battalion launched a rain of mortar shells with the devastating effect that its front area was covered with bodies. When the Chinese communists continued to bring in fresh troops in the attack, the Belgian-Luxembourg troops fought a successful delaying battle which enabled the adjoining positions to be methodically evacuated with minimum losses.

The Belgian battalion with the Luxemburg detachment has shown so much proof of courage, decision and esprit de corps in the accomplishment of its missions during these actions in difficult and hazardous circumstances, that it has to be placed above any other units participating in these actions. The extraordinary courage shown by the members of this units during this period has bestowed extraordinary honor on their country and on themselves.

South Korea would add their own Presidential Unit Citation to the Belgian-Luxembourg unit, and a second US Citation would be awarded for actions at Haktanhni in October, and would remain in Korea through 1953, with two KIA, 17 WIA, and having had no men missing or captured.

Source: 'United Nations Participants in the Korean War: The Contributions of 45 Member Countries' by Paul M. Edwards

'Understanding the Korean War' by Arthur H. Mitchell

That's super interesting. Thank you!