Army Special Forces is the only combat arms element in the US military that requires every member to have some mastery of a foreign language:
Why not just use interpreters?
Well, can you trust an interpreter the way you can a team member? Maybe. In time. With a certain subset of interpreters. But right from the beginning? No.
You also need to have linguists on the team as a safety check on those interpreters. If they think they can get away with it, they’re going to put their own spin on what you’re saying — at the very least. It’s human nature.
But some people find language learning inordinately hard. We don’t know the neuropsychiatric explanation for this, but some bright people struggle to learn a language, just like some people are (at least in their youth) natural language sponges. It seems to be correlated with verbal reasoning in one’s native language, but not perfectly (or it would track IQ, most measures of which are half dependent on verbal reasoning). So there is a Language Aptitude or “L” factor which is only weakly correlated with Spearman’s “G” factor of general intelligence.
The Army (and now DOD) has a test that purports to measure one’s language aptitude. It’s recently been subject to a little drama, as the test scores tend to have a correlation with race, which is anathema to all right-thinking people, but so far they have not race-normed the scores (i.e., provided some affirmative action points to popular ancestries). Your performance on the DLAB, Defense Language Aptitude Battery is a usable indicator, albeit an imperfect one, of your general “L” factor, and the military will often assign languages based on DLAB performance. (The military assesses languages in Categories. Cat I is an easy language, for an English speaker, like Spanish or French. Cat IV is a tough one, like Chinese Mandarin or Arabic). For an 18X starting out in Special Forces, your language may also determine what Group you go to, although all bets are off in time of war. A trainee may get an opportunity to pick the language from within the category, depending on the needs of the Army. So if you’re a Category III, picking Russian might get you assigned to Europe-oriented 10th Group (although some Russian speakers are needed in other groups). Pick Chinese or Korean, and you will be wearing the yellow flash of the 1st Group; select Farsi, and you’ll be wearing the freshly-restored Vietnam-era flash of the 5th. Or a trainee may just be told “You start language school Monday. Roster Number 107, to French. Roster 116…”
People who scored high on the DLAB often find language learning easier than people who scored low. There’s a mountain of data on this after decades of DLABs. While the cut-off score for Cat I languages in 95, cut-off scores are a bit rubbery… if they don’t have enough students to fill a class, they may bend on admissions requirements. This bending often does the candidate no favors. Few people with scores below 100 complete a long-term language school like DLI, although with good study habits, hard work, and self-discipline, someone with limited aptitude can bull through the shorter SF language school. And the higher the score, the better. While you can get into a Cat IV language school with a 110, the cluster of people down around the minimum score are often not there on graduation day.
Of course, SF and other linguist positions in the military sometimes luck into a native speaker. This is a good thing, subject to CI investigation of the student and his or her family. (If the CI work is botched, you get situations like the Naval flight officer now sitting in the brig, charged with spying for China).
Not everyone in SF thinks language is worthwhile.
This idea tends to be concentrated in the officer corps, especially in those who have spent much of their career in Direct Action units (like the Rangers, for one example). One such officer was Colonel (later Brigadier General) Frank J. Toney, who had been a protegé of James Guest, in an environment where only door-kicking counted. When Toney took over SF Command, he brought his attitude with him: “My men don’t need any language training. They can speak 5.56 and 7.62!”
We leave as an exercise for the reader, why his nickname was Blank Frank.