TEMPORARY TWR WITH NO CLASS D AIRSPACE.

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I SUBMIT THIS TO RPT AN UNUSUAL OCCURRENCE I HAVEN'T SEEN BEFORE. I WAS FLYING AS PART OF A MIL EXERCISE THAT WAS USING A LNDG ZONE APPROX 10 MI S OF ALLEN ARMY AIRFIELD. ONE OF THE NOTAMS FOR TODAY'S MISSION WAS THAT ALLEN FIELD HAD ESTABLISHED A TEMPORARY ATC TWR BUT THE AIRSPACE AROUND THE FIELD WAS STILL CLASS E; NOT CLASS D. COMS WITH THE TWR WERE NOT REQUIRED ACCORDING TO OUR MISSION BRIEFER. MY PLAN WAS TO MONITOR ALLEN'S TWR FREQ FOR TA'S BUT NOT CONTACT THEM DIRECTLY SINCE WE WOULD NOT BE TRANSITING CLOSE ENOUGH TO INTERFERE WITH THE TFC PATTERN. THE CLOSEST WE GOT TO ALLEN WAS 4 NM. AT THAT TIME; ALLEN TWR CALLED US ASKING FOR US TO IDENT OURSELVES AND STATE OUR INTENTIONS. ALLEN RESPONDED WITH A 'ROGER.' I THEN CONFIRMED WITH THEM THAT THE AIRSPACE WAS CLASS E; AND NOT CLASS D. THEY CONFIRMED THIS BUT DID NOT CLARIFY AS TO HOW A TWR COULD EXIST TO CTL CLASS E AIRSPACE. ALTHOUGH THERE WAS NO TFC IN THE ALLEN FIELD AREA AT THE TIME AND ALLEN TWR DID NOT SEEN CONCERNED THAT WE WERE OPERATING IN THEIR VICINITY WITHOUT CONTACTING THEM; I THOUGHT THE EVENT UNUSUAL ENOUGH TO TAKE THE PRECAUTION OF FILING THIS RPT. I GUESS WHAT'S CONFUSING IS TRYING TO FIGURE OUT WHAT'S REQUIRED WHEN OPERATING N CLASS E AIRSPACE EVEN THOUGH A TWR IS OPERATING.