These are all the MOS's on the critical MOS list in the last MILPER message (20 February 2009)
11B INFANTRYMAN
11C INDIRECT FIRE INFANTRYMAN
13B CANNON CREWMEMBER
13F FIRE SUPPORT SPECIALIST
13M MLRS/HIMARS CREWMEMBER
13P MLRS AUTOMATED TACTICAL DATA
13R FIELD ARTILLERY (FA) FIREFINDER RADAR OPERATOR
13S FIELD ARTILLERY SURVEYOR
14J AIR DEFENSE COMMAND, CONTROL, COMMUNICATIONS, COMPUTERS AND INTELLIGENCE TACTICAL OPERATIONS CENTER ENHANCED OPERATOR/MAINTAINER
15B AIRCRAFT POWERPLANT REPAIRER
15J OH-58D/ARH ARMNT/ELECTRICIAN/AVN SYS REPR
15Q AIR TRAFFIC CONTROLLER
19D CAVALRY SCOUT
19K M1 ARMOR CREWMAN
21B COMBAT ENGINEER
21D DIVER
21C BRIDGE CREWMEMBER
21E CONSTRUCTION EQUIPMENT OPERATOR
21Y GEOSPATIAL ENGINEER
25B INFORMATION TECHNOLOGY SPECIALIST
25L CABLE SYSTEM INSTALLER-MAINTAINER
25N NODAL NETWORK SYSTEM OPERATOR-MAINTAINER
25P MICROWAVE SYSTEMS OPERATOR-MAINTAINER
25R VISUAL INFORMATION EQUIP OPER/MAINT
25U SIGNAL SUPPORT SYSTEMS SPECIALIST
25V COMBAT DOCUMENTATION/PRODUCTION SPECIALIST
27D PARALEGAL SPECIALIST
31B MILITARY POLICE
31E INTERNMENT/RESETTLEMENT SPECIALIST
35F INTELLIGENCE ANALYST
35L COUNTERINTELLIGENCE AGENT
42R ARMY BANDPERSON w/ASI 9B, 9D, 9J, 9N, 9T, OR 9U ONLY
45G FIRE CONTROL REPAIRER
46Q PUBLIC AFFAIRS SPECIALIST
46R PUBLIC AFFAIRS BROADCAST SPECIALIST
56M CHAPLAIN ASSISTANT
62B CONSTRUCTION EQUIPMENT REPAIRER
63B WHEELED VEHICLE MECHANIC
63H TRACK VEHICLE REPAIRER
63J QUARTERMASTER AND CHEMICAL EQUIPMENT REPAIRER
63M BRADLEY FIGHTING VEHICLE SYSTEM MAINTAINER
68S PREVENTIVE MEDICINE SPECIALIST
68T ANIMAL CARE SPECIALIST
68W HEALTH CARE SPECIALIST
74D CHEMICAL, BIOLOGICAL, RADIOLOGICAL, NUCLEAR (CBRN)
SPECIALIST
88M MOTOR TRANSPORT OPERATOR
88N TRANSPORTATION MANAGEMENT COORDINATOR
89A AMMUNITION STOCK CONTROL AND ACCOUNTING SPECIALIST
92F PETROLEUM SUPPLY SPECIALIST
92G FOOD SERVICE SPECIALIST
92R PARACHUTE RIGGER
92W WATER TREATMENT SPECIALIST
94D AIR TRAFFIC CONTROL EQUIPMENT REPAIRER
94E RADIO AND COMMUNICATIONS SECURITY (COMSEC) REPAIRER
94Y INTEGRATED FAMILY OF TEST EQUIPMENT (IFTE) OPERATOR AND MAINTAINER
http://armyreenlistment.com/Messages/MILPER/SRB_Enhanced_09_028_20090213.pdf If he's prior service he will either have to go back to his prior MOS or pick from a crital MOS (the list I posted)