First, you have a support order issued by a court? If not there's nothing you can do until you get one.
After you get an order of support you can contact the army (Not "JAG" and not his "CO") and get the order enforced either by a forced allotment or a wage garnishment.
Here's an article telling how to get the money once you have a court order of support.
http://www.acf.hhs.gov/programs/cse/fct/militaryguide2000.htm#collect
COLLECTING SUPPORT FROM MILITARY PERSONNEL
Collecting child support from military personnel is generally governed by military regulations. See Army, 32 C.F.R. Part 584, Army Regulation 608-99, 1 Nov 94; Navy/Marine Corps, 32 C.F.R. Part 733; and Air Force, 32 C.F.R. Part 818.
These regulations require military personnel to pay child support in accordance with support agreements and court orders. In the absence of a court order or support agreement, Army and Marine regulations criminalize failure to pay support at a level generally equivalent to a member's authorized "Basic Allowance for Housing (BAH)." All other services have established guidelines in the regulations for use by the commander where there is no court order or support agreement.
Under military regulations, one solution is a voluntary allotment. Pleas note, however, a voluntary allotment is completely under the member's control and can be started, stopped, or amended at will. A voluntary allotment is a convenience that the government provides military personnel to help them to meet their obligations.
Be advised that without some sort of allotment, child support enforcement is largely outside of a commander's discretion. Commanders cannot direct that a member's pay be diverted to family members, even if a court order exists; a commander can only punish a member for failure to comply. Best Practice Tip #14: Obtaining a court or administrative court is critically important. With a court order, a family can receive child support withheld involuntarily from military personnel through use of garnishments, involuntary allotments, and/or wage assignments.
For use of Garnishments, see 42 U.S.C. §§ 659-662; 5 C.F.R. Part 581. The allowable bases for garnishments include enforcement of periodic family support obligations (including costs and attorney fees if State law defines these items as components of "support").
Pay subject to garnishment generally includes: (1) Federal civilian employee pay and retirement annuities; (2) military active duty pay (basic pay and certain bonuses, but not BAH and BAS/Sep Rats); (3) military retired pay; (4) military reserve pay; and (5) any other "remuneration for employment."
The amount subject to garnishment is the lower of State or Federal ceilings. The Federal ceiling is 50 percent to 60 percent of net pay, depending on the family situation and length of time in arrears; arrears in excess of 12 weeks adds another five percent.
Procedures require obtaining a garnishment order from a State court (naming the employing Federal agency as garnishee) and serving the order, with a copy of the underlying support order, on the employing agency by registered or certified mail; include member's name, status (i.e., active duty, civilian, retiree) and the member's Social Security Number. See Appendix G for Addresses for Serving Orders.
The member's defenses against garnishment include garnishment for impermissible purpose; garnishor's noncompliance with 5 C.F.R. Part 581; subsequent litigation enjoining the garnishment; and possibly an appeal of the underlying support order, depending on the State's laws.
For the use of Involuntary or Mandatory Allotments, see 42 U.S.C. § 665; 32 C.F.R. Part 54. Involuntary allotments are essentially wage withholding actions enforceable against active duty military pay (basic pay, plus bonuses, plus BAH and BAS in some cases).
Best Practice Tip #15: Involuntary allotments are almost always superior to garnishment actions. Involuntary allotments tend to be easier to obtain, longer lasting, and more lucrative in terms of meeting support obligations.
The prerequisites for involuntary allotments begin with a court or administrative order establishing a child support (or spousal and child support) obligation and an arrearage in an amount equal to or greater than two months support under the order.
The procedure for establishing involuntary allotments begins with a "Notice" from any court or any State CSE agent to the military requesting initiation of an involuntary allotment. The Notice can simply be a letter. See Appendix H for a sample notice. No prior notice to the obligor is necessary. The Notice is sent by registered or certified mail to the same officials as for garnishments (see Appendix G).
The Notice should include the member's full name and Social Security Number; a statement that there are arrearages equal to or greater than two months child support; a copy of the underlying order certified by the Clerk of the Court (or by the head of the administrative agency if an administrative order); the date the allotment should stop; and a statement certifying the writer is an "authorized person" or a State CSE agent.
The involuntary allotment will only be for the amount of the monthly support obligation. If arrearages are sought, they must be requested and there must be a court or administrative order which specifically requires the payment of accrued arrearages. There are limitations on the amount of involuntary allotments, which are the same as the limits for garnishment (50 percent to 60 percent, plus five percent if 12 or more weeks in arrears).
The member's defenses against involuntary allotments require that the defendant establish by affidavit and evidence that the underlying child support order has been vacated or modified or that the amount alleged to be in arrears is erroneous.
Be advised that administrative wage assignment withholding notices that are based on a conditional court order and an arrearage sometimes are not honored by military pay offices; they may insist on a subsequent order issued by a court. When sending an administrative withholding order, include a copy of the applicable statute to show that it constitutes valid "process" under State law. Best Practice Tip # 16: Military pay offices almost always honor automatic wage withholding orders (i.e., those that take effect whether or not there is an arrearage).
Send State wage assignment withholding orders to the same office as garnishment orders (see Appendix G). Compensation subject to withholding includes basic pay and bonuses, but not BAH or BAS/Sep Rations. The amount of compensation withheld is limited to 50 percent – 60 percent plus five percent if 12 or more weeks in arrears.
The Uniformed Services Former Spouses' Protection Act (see 10 U.S.C. § 1408; 32 C.F.R. Part 63) essentially authorizes wage withholding against military retired pay for child support and/or spousal support obligations created by a final decree of divorce or legal separation (but not a paternity decree).
No arrearage is necessary to trigger the withholding; the former spouse can initiate a direct payment simply by written request to the appropriate finance center (see Appendix G). The right to receive direct payment is personal to the former spouse and cannot be assigned to a CSE agency, although a request for payment through such an agency may be honored.
The primary alternatives to using this Act to collect child support from retired pay are garnishments and State wage withholding orders.