This article from Strategy Page has some interesting facts about foreigners serving in the US (and other country's) militaries. Here's an excerpt:
In the last decade the U.S. military has enlisted some 70,000 non-citizens, about five percent of all recruits. These foreigners made better soldiers than American citizens. The foreigners are tossed out during their first three months of service at half the rate of their citizen counterparts. After three years of service 72 percent of citizens were still in uniform, compared to 84 percent of non-citizen troops. The foreign troops are more patriotic and work harder than their citizen counterparts.
It's also interesting to note that more Latinos have been awarded the Medal of Honor (the highest military decoration awarded by the US government), than any other ethnic group.
Because I'm not a racist or tribalist, I don't think there is something inherent in Latino genes that makes them a better soldier than a person of German or Irish descent, for example. I think it has more to do with the work ethic of immigrants vs. the native-born American.
Many native-born Americans now believe they have a right to a job, a right to health care and a right to the American way of life, but they don't. This country was founded under mostly capitalist ideals, including that you have to earn what you desire. You have the right to pursue your happiness, but happiness and prosperity is not automatic.
Immigrants seem to really understand that concept and they are willing to do just about any job in order to exercise their right to pursue happiness. They will work jobs Americans aren't willing to work, and save what little money they earn in an attempt to move up in the world, and that's incentive to do their work very well!