RC-135 MIL TANKER TURNS TO WRONG HDG RESULTING IN A TCASII TA AND CORRECTIVE HDG FROM ZMP.

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I WAS THE ACFT COMMANDER (PIC) OF RECORD. THE REMAINING FLT DECK CREW INCLUDED ANOTHER RECENTLY REQUALIFIED; INSTRUCTOR; QUALIFIED ACFT COMMANDER (IP2); 1 CO-PLT; AND 2 INSTRUCTOR NAVIGATORS. AFTER LEVELOFF; I LEFT THE FLT DECK TO GO TO USE THE BATHROOM. DURING MY ABSENCE FROM THE FLT DECK; THE 2 INSTRUCTOR NAVS ASKED THE PLTS TO OBTAIN AN AMENDMENT TO THE FILED FLT PLAN FROM ZMP IN ORDER TO UPDATE TIMING TO AN AIR REFUELING TRACK. WHILE THE PLTS WERE OBTAINING THE AMENDED CLRNC ON 1 RADIO; THE NAVIGATORS BEGAN COORDINATING WITH THE TANKER FORMATION ON A SEPARATE RADIO. WHILE THE NAVIGATORS WERE STILL COORDINATING WITH THE TANKERS; ZMP GRANTED THE AMENDED CLRNC. IP2 ELECTED TO COMPUTE THE HDG TO THE AMENDED POINT USING HIS TACAN. HOWEVER; DUE TO AN IMPROPERLY PLACED SWITCH (TACAN SELECT); HIS COMPUTED HDG WAS INCORRECT AND HE TURNED THE ACFT TO A HDG OF APPROX 360 DEGS (THE CORRECT HDG WAS 275 DEGS). SHORTLY AFTER ROLLOUT ON THIS HDG; THE CREW RECEIVED TA ADVISORY ('TFC; TFC') ON THE TCASII. AT THIS TIME; I RETURNED TO THE FLT DECK TO FIND THE OTHERS SCANNING FOR THE AIR TFC. AFTER PLUGGING BACK INTO THE INTERPHONE; I NEXT HEARD ZMP CALL TO DIRECT US TO TURN R TO A HDG OF 280 DEGS (270 DEG TURN). THEY NEXT QUERIED WHY WE WERE ON A 360 DEG HDG. IP2; REALIZING HIS MISTAKE; SUGGESTED AND THE CO-PLT THEN RELAYED TO ARTCC THAT WE HAD MADE A 'NAV ERROR.' HUMAN PERFORMANCE FACTORS: FAILURE TO SELECT THE TACAN IS SOMEWHAT COMMON IN THIS ACFT (ERGONOMIC FACTOR). EVERY RC-135 PLT HAS MADE THIS SAME MISTAKE AND MORE THAN ONCE. ALSO; BETTER SITUATIONAL AWARENESS WOULD HAVE PRECLUDED A TURN TO THE N; SINCE THE BEGINNING OF THE AIR REFUELING TRACK WAS DUE W OF THE ACFT'S POS. ADDITIONALLY; THE NAVIGATORS BECAME SO DISTR WITH THE TANKER COORD; THAT THEY WERE NOT EVEN INITIALLY AWARE THAT ARTCC HAD GRANTED THE CLRNC AMENDMENT OR THAT THE PLT HAD TURNED THE ACFT. THE CO-PLT DID NOT DOUBLECHK IP2'S HDG EVEN THOUGH HIS NAV INSTS WERE CORRECTLY SET. IN SHORT; THE CREW EXPERIENCED; AT PRECISELY THE WRONG TIME; A SHORT LIVED; MOMENTARY BREAKDOWN IN CRM. THERE WERE A NUMBER OF PLACES WHERE; IF SOMEONE HAD INTERVENED; THIS SIT COULD HAVE BEEN AVOIDED. IP2 DID NOT MAKE USE OF THE COMPUTERIZED FLT PLAN OR PLT'S CHART TO MAINTAIN HIS SITUATIONAL AWARENESS WITH RESPECT TO THE ACFT'S COURSE. ADDITIONALLY; HE SHOULD HAVE INTERRUPTED AT LEAST ONE OF THE NAVIGATORS WHILE THEY WERE SPEAKING TO THE TANKER; TO CONFIRM THE CORRECT HDG. THE CO-PLT; EVEN THOUGH HE HAD SET UP HIS NAV INSTS CORRECTLY; EITHER FAILED TO COMPUTE THE HDG ON HIS OWN (FOR XCHK PURPOSES) OR ELECTED TO NOT SAY ANYTHING ABOUT THE INCORRECT HDG. BOTH NAVIGATORS ALLOWED THEMSELVES TO BECOME SO OVERLY DISTR WITH TANKER COORD; THAT THEY COMPLETELY NEGLECTED THE MORE IMMEDIATE TASK OF FLYING THE AIRPLANE. I; AS THE MORE EXPERIENCED ACFT COMMANDER AND INSTRUCTOR PLT; SHOULD HAVE ANTICIPATED THE POSSIBLE REQUIREMENTS AND DEMANDS ON THE CREW AND REMAINED ON THE FLT DECK UNTIL WE HAD RESOLVED THE TIMING AND COORD WITH THE TANKERS; OBTAINED THE NEW ATC CLRNC; AND HAD TURNED THE ACFT TO THE CORRECT HDG.