POTENTIAL CONFLICT AFTER UNAUTH PENETRATION OF AIRSPACE BY MIL ACFT. PROX OF ATA.

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CLRED BY DULLES APCH FOR ILS APCH 26 AT MARTINSBURG VIA MRB VOR; TRANSITION RTE TO FAF. AFTER INTERCEPTING ILS FINAL; DULLES ADVISED OF VFR TFC IN VICINITY OF ARPT; TERMINATED RADAR SVC AND TOLD US TO CONTACT TWR. WE SWITCHED FREQ IMMEDIATELY; BUT WERE PREOCCUPIED WITH LNDG CHKLIST AND SEARCHING FOR TFC AND DIDN'T CALL TWR RIGHT AWAY. AT APPROX 4 MI OUT; I SAW A LOW WING SINGLE ENG ACFT TURNING TO FINAL AT ABOUT OUR 10 O'CLOCK IN A BANK SUCH THAT I DON'T THINK HE SAW US. HE WAS INTERCEPTING FINAL AHEAD OF US (BELLY-UP TO US); SO I INITIATED A CLBING L TURN TO GAR BEHIND HIM. AT THIS TIME THE ACFT COMMANDER WAS CALLING THE TWR OPERATOR; WHO WAS VERY SURPRISED BY OUR APPEARANCE AND UPSET THAT WE HAD NOT CALLED EARLIER. SHE WAS VERY RIGHT! WE ALLOWED OUR COM DISCIPLINE TO BREAK DOWN DUE TO PREOCCUPATION WITH CHKLISTS AND DISCUSSING OF THE TFC AND THE APCH. WE ALSO ASSUMED; WRONGFULLY; THAT THE TWR WOULD RECEIVE A RADAR HDOF FROM DULLES APCH. THE MEANING OF 'RADAR SVC TERMINATED' HAD NOT SUNK INTO OUR CONSCIOUSNESS. OUR SUBSEQUENT DISCUSSION OF THIS INCIDENT HAS SERVED AS A GOOD REVIEW OF COMS AT CTAF (TWR) FACILITIES.