All 4 branches train at Defense Language Institute, Presidio of Monterey, California. The basic Russian course was 47 weeks long when I went through in 1979.
I served 4 years in the Navy as an Airborne Direct Support Russian Voice Intercept Operator (Cryptologic Technician, Interpretive branch) and flew with Fleet Air Reconnaisance Squadron 2 (VQ-2) out of Rota, Spain. After I returned home, I joined the Army Reserves and completed training to work as a Russian Interrogator.
I hear that Russian is not in as much demand as it was when I joined...You might expect to be offered Arabic or Farsi if you pass the DLATB.