Part of the problem would be the identification of Korean as a target language, the identification of reliable people to use as instructors, and the standards required of the linguists to use them as the necessary intelligence functionaries -- interrogators, order of battle analysts, and voice interceptors/translators/cryptanalysts.
I don't think DLI got its full boat of schools going until the late 1950s when we began to realize there were a lot of hostile types out there who we needed to track. Russian and Chinese were (and still remain) "Tier 1" languages or high density ones for training. Vietnamese was added in the late 1960s but dropped way back after 1973 (which is why I got retrained from Vietnamese into Russian).
The schools were (according to some of the history we were taught ) training linguists in courses of around 1 year in length, and required either some college or graduates as the linguists were commissioned during WWII. Afterwards the volume went up and the level of rank commensurate with the job went down -- the last "mandatory" rank awarded was SP5 or SGT upon graduation, and that died in July 1969.
DLIWC has been training in Korean for many years now, but Korean linguists are still in short supply. Problem is there is no place to go except in a track from Korea to a US unit to Korea to the US... Unless you really love the languange, you don't stay in. We have seen some "native" speakers in recent years, though, as immigrants go into second generations and they join the services. But would bet in 1950 the numbers were very, very low.