What was found
DECLARED EMERGENCY AND AIR TURNBACK, SHORTLY AFTER T/O FWD CARGO BAY FIRE ALARM LIGHT ILLUMINATED WITH AUDIO ALARM. EXECUTED THE CHECKLIST, FIRED BOTH BOTTLES. INSPECTED FWD CARGO BIN, NO EVIDENCE OF FIRE OR OVER HEATING. OK TO CONTINUE PER MEL. LATER AT BWI, REMOVED AND REPLACED CCU, FIRE BOTTLES, METERING VALVE, DIVERTER VALVE AND 4 EA SDU'S FOR FWD CARGO. PERFORMED PRESS LEAK AND FIRE SUPPRESSION SYSTEM FUNCTIONAL TEST PER MM. SYSTEM TEST NORMAL, NO FAULTS FOUND.