During WWII the Americans had to "produce" efficient speakers of german, japanese and russian very quickly. With not that many Germans willing to help, they developped methods using audio tapes that the intelligence officers (language learners) could use without teachers, saving these for advanced students. The programs were centered on dialogs to be learned by heart and, not surprisingly, drills that stressed patterns of speech (phrase structures). The system was so efficient that after 6 months the officers could begin active work.

These efforts were at the beginning of the Defense Language Institute in Monterrey (California), which nowadays teaches 10% of all adult language courses in the USA.

(Note : if you know more about this, or have been involved in this program, I would be really glad to hear from you at Francois@micheloud.com)