POTENTIAL CONFLICT BTWN 2 DEP ACFT. SEE AND AVOID CONCEPT WORKED; FOR 1 ACFT.

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GPT TWR ASSIGNED TKOF HDG 360 DEGS; MAINTAIN AT OR BELOW 1500 FT; CONTACT DEP. WE DID SO IN SEQUENCE. DURING THE CLB AT ABOUT 800 FT MSL; DEP DESCRIBED A MIL C-12 (KING AIR 200) DEPARTING BEHIND US OFF RWY WHO 'HAD US IN SIGHT AND WOULD MAINTAIN VISUAL SEPARATION.' MY CREW ACQUIRED THE C12 ALSO AND RPTED THAT. WE WERE THEN GIVEN A L TURN TO 340 DEGS. WE WERE WATCHING THE C12 CLB WHEN HE ENTERED A R TURN AND PROCEEDED ACROSS OUR FLT PATH IN A TRAJECTORY WHICH WOULD HAVE BEEN AT OUR ALT HAD THE CLB CONTINUED. I INITIATED A RAPID DSCNT AND DECELERATION TO PASS WELL BELOW AND BEHIND THE C12. THE FLT CONTINUED UNEVENTFULLY TO DEST. MY CREW WAS NOT SURE WHAT INSTRUCTIONS WERE GIVEN TO THE C12 BUT WE WERE SURE THAT DEP ADVISED US THAT THE C12 HAD US IN SIGHT AND WOULD MAINTAIN VISUAL SEPARATION. THE C12 NEVER APPEARED TO HALT HIS CLB OR MANEUVER AWAY FROM AN INTERSECTING FLT PATH WITH MY ACFT. WE DID NOT CARE SINCE WE HAD THE CAPABILITY TO AVOID REALLY CLOSE PROX; AND DID SO PROMPTLY. IT MAY BE THAT THE RAPID INSTRUCTIONS AND TRANSFER OF CTLRS FAILED TO INDICATE WHO WAS MAINTAINING SEPARATION FROM WHOM; CLRLY; TO THE C12. I CREDIT MY CREW CHIEF AND OUR UNIT COCKPIT RESOURCE MGMNT PROGRAM FOR EARLY DETECTION OF THE C12 AND RAPID CONFLICT RESOLUTION.