32 C.F.R. § 516.49 – Expert witnesses.

(a) General rule. Present DA personnel will not provide, with or without compensation, opinion or expert testimony either in private litigation or in litigation in which the United States has an interest for a party other than the United States. Former DA personnel will not provide, with or without compensation, opinion or expert testimony concerning official information, subjects, or activities either in private litigation or in litigation in which the United States has an interest for a party other than the United States. (See figure G-3, appendix G of this part). An SJA or legal adviser is authorized to deny a request for expert testimony, which decision may be appealed to Litigation Division.
(b) Exception to the general prohibition. If a requester can show exceptional need or unique circumstances, and the anticipated testimony will not be adverse to the interests of the United States, Litigation Division may grant special written authorization for present or former DA personnel to testify as expert or opinion witnesses at no expense to the United States. In no event may present or former DA personnel furnish expert or opinion testimony in a case in which the United States has an interest for a party whose interests are adverse to the interests of the United States.
(c) Exception for AMEDD personnel. Members of the Army medical department or other qualified specialists may testify in private litigation with the following limitations (See figure G-4, appendix G, of this part):
1. (1) The litigation involves patients they have treated, investigations they have made, laboratory tests they have conducted, or other actions taken in the regular course of their duties.
2. (2) They limit their testimony to factual matters such as the following: their observations of the patient or other operative facts; the treatment prescribed or corrective action taken; course of recovery or steps required for repair of damage suffered; and, contemplated future treatment.
3. (3) Their testimony may not extend to expert or opinion testimony, to hypothetical questions, or to a prognosis.
(d) Court-ordered expert or opinion testimony. If a court or other appropriate authority orders expert or opinion testimony, the witness will immediately notify Litigation Division. If Litigation Division determines it will not challenge the subpoena or order, the witness will comply with the subpoena or order. If directed by Litigation Division, however, the witness will respectfully decline to comply with the subpoena or order. (See United States ex. rel. Touhy v. Ragen, 340 U.S. 462 (1951)).
(e) Expert witness fees. All fees tendered to present DA personnel as an expert or opinion witness, to the extent they exceed actual travel, meals, and lodging expenses of the witness, will be remitted to the Treasurer of the United States.