On February 9, 2015, the Court of Appeals for Veterans Claims (CAVC) issued an opinion stating “[as] urged by the veteran, that [38 C.F.R.] § 3.309(a) includes tinnitus, at a minimum where there is evidence of acoustic trauma, as an “organic disease of the nervous system.” That decision can be accessed at Fountain 13-0540 (Fountain v. McDonald). In essence, the CAVC overturned a provision in VA Training Letter 10-02 (Adjudicating Claims for Hearing Loss and/or Tinnitus) that found that “unlike hearing loss, tinnitus may not be service-connected as a presumptive condition under 38 C.F.R. § 3.309(a) because it is a subjective symptom rather than an organic disease of the nervous system.”
In rejecting the Secretary’s argument, the CAVC further held that nothing “preclude[es] establishing service connection for tinnitus on the basis of continuity of symptomatology  and the appellant is not precluded from seeking VA benefits for his claimed tinnitus by way of the chronicity or continuity-of-symptomatology provisions of §§ 3.303 and 3.309(a).”
I’m aware that many veterans and advocates have had trouble finding an access point on the Internet for VA TL 10-02 and the Military Occupational Specialty (MOS) Noise Exposure Listing [which includes MOSs for USMC/AF/NA/USCG]. I’ve uploaded those documents at Duty MOS Hearing Loss Probability Chart-VA Fast Letter 10-35 and VA Training Letter 10-02.