MIL C130 ACFT PREPARING FOR DEP; WAS GIVEN ANOTHER ACFT'S DEP INSTRUCTIONS. BOTH ACFT HAD SIMILAR CALL SIGNS.

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DURING THE MORNING BRIEF FOR THE AIRDROP WE WERE TOLD THAT IT IS NORMAL TO FILE THE TIGER S DEP (WITH A R TURN AFTER TKOF). THE TIGER N IS A L TURN AFTER TKOF. WE LOOKED AT THE LCL OPS GUIDE AND DETERMINED THAT THIS WAS THE BEST WAY TO FILE (A TIGER S WAS FILED -- A R TURN OUT). DURING TAXI FOR TKOF THE CLRNC WAS RECEIVED -- THERE WAS SOME CREW MEMBER CONVERSATION FROM THE CREW DURING THIS; HOWEVER THE CLRNC WAS READ BACK CORRECTLY. I ASKED IF THAT WAS A R TURN OUT AND THE COPLT'S RESPONSE WAS YES. OUR CALL SIGN WAS ABC AND TOOK OFF AND FLEW OUR FILED DEP. TWR TOLD US WE DID NOT FLY THE DEP GIVEN OR FILED. WE TOLD THEM THAT THIS IS WHAT WE FILED NOT A L TURN. AFTER RETURNING I CALLED TWR ON THE PHONE; THERE WERE 2 ABC'S IN THE SYS AND WE GOT THEIR CLRNC; NOT OURS. THE TWR SUPVR SAID DUAL CALL SIGNS HAD BEEN A TREND AT POPE HOWEVER; COMMAND POST IN CHARGE OF DE-CONFLICTING THE CALL SIGNS WHICH THEY THEMSELVES DETERMINE SAID IT WAS NOT A PROB. I SUGGESTED THAT THE C130'S USE DIFFERENT CALL SIGN AS WELL AS NUMBERS -- NOT JUST CHANGE THE NUMBERS. PS: WE HEARD THE OTHER ABC AS WE WERE TAXIING FOR TKOF ON GND FREQ.