(a) General. The basic considerations relating to service connection are stated in § 3.303. The criteria in this section apply only to disabilities which may have resulted from service other than in a period of war before January 1, 1947.

(b) Presumption of soundness. A peacetime veteran who has had active, continuous service of 6 months or more will be considered to have been in sound condition when examined, accepted and enrolled for service, except as to defects, infirmities or disorders noted at the time thereof, or where evidence or medical judgment, as distinguished from medical fact and principles, establishes that an injury or disease preexisted service. Any evidence acceptable as competent to indicate the time of existence or inception of the condition may be considered. Determinations based on medical judgment will take cognizance of the time of inception or manifestation of disease or injury following entrance into service, as shown by proper service authorities in service records, entries or reports. Such records will be accorded reasonable weight in consideration of other evidence and sound medical reasoning. Opinions may be solicited from Department of Veterans Affairs medical authorities when considered necessary.

(c) Campaigns and expeditions. In considering claims of veterans who engaged in combat during campaigns or expeditions satisfactory lay or other evidence of incurrence or aggravation in such combat of an injury or disease, if consistent with the circumstances, conditions or hardships of such service will be accepted as sufficient proof of service connection, even when there is no official record of incurrence or aggravation. Service connection for such injury or disease may be rebutted by clear and convincing evidence to the contrary.