Service connection for hearing loss requires the same three elements as any VA claim: (1) a current diagnosis of hearing loss (audiogram showing measurable impairment), (2) an in-service event — virtually always noise exposure, and (3) a nexus connecting the in-service event to the current hearing loss. For most noise-exposed veterans, element (2) is the strongest: the MOS, AFSC, or naval rate documents the noise environment without requiring a separate letter.
MOS noise exposure — the most common in-service noise hazard billets
Army: Infantry (11 series), Field Artillery (13 series), Cavalry (19 series), Special Forces (18 series), Aviation (15 series), Combat Engineers (12 series), Armor (19K/E). Crew-served weapons (M2HB, M240, M249), howitzers, main battle tanks, and mortar systems produce sustained noise levels above 140 dB — far above safe exposure thresholds.
Navy / Marine Corps: Engineering ratings (EN, MM, BT, EM), aviation ratings (AD, AE, AM, AO, AV), gunner's mates, flight deck crew, submarine machinery spaces, shipboard combat systems, Marine Corps infantry and weapons MOSs (0311, 0331, 0341, 0351), and any billet requiring regular flight deck or flight line work.
Air Force: Aircraft maintenance (2A-series), airfield and flight line specialties, munitions (21M), security forces in flight-line environments, crew chiefs, aircraft loadmasters, and explosive ordnance disposal (EOD).
Coast Guard: Machinery technicians (MK), maritime enforcement, flight mechanics on rotary wing aircraft, and any billet near marine diesel engines.
The Hickson elements for noise-induced hearing loss service connection: (1) history of occupational or recreational noise exposure, (2) audiometric pattern consistent with noise-induced hearing loss (4000 Hz notch on audiogram is the classic fingerprint), and (3) exclusion of non-noise causes. Your MOS documentation, personnel record, and any fitness reports mentioning duty assignments establish elements 1 and 2. A private audiologist can attest to element 3 in a nexus letter.
Buddy statements — the underused evidence for noise exposure claims
Service members almost never reported hearing problems during service — it was normalized and reporting it meant being removed from duty. The absence of medical records documenting hearing complaints does not mean the exposure didn't happen. VA Form 21-10210 buddy statements from fellow veterans who served in the same unit, operated the same equipment, or worked in the same noise-hazardous environment can directly corroborate your exposure history. A buddy statement doesn't need to say your hearing is damaged — it only needs to corroborate the noise exposure ("We fired the M198 howitzer multiple times per week at [training site] from [year] to [year] and hearing protection was not always available or consistently used").
Buddy statements are especially valuable when your service record lists a billet or MOS that is not on the obvious noise-hazard list but where the actual working environment was loud — motor pool, vehicle maintenance, shipboard spaces. The buddy statement describes the actual working conditions, not just the job title.
If you need stronger nexus evidence — especially if you've already been denied — a private audiologist's independent medical opinion (IMO) is the cleanest path. The letter should: (1) review your audiogram and note the noise-induced pattern (high-frequency loss at 4000 Hz), (2) identify your MOS/service history as noise exposure documentation, and (3) state that your hearing loss is "at least as likely as not" related to in-service noise exposure. The 50% standard — "at least as likely as not" — is the legal threshold. The opinion doesn't need certainty.