Boeing—E-3 Sentry: USAF Variants and Serials Original construction designations E-3A: The first two aircraft were allocated the designation EC-137D although this was changed to E-3A shortly after the maiden flight of the first aircraft. Twenty-five E-3As were purchased between 1971 and 1979. · 71-1407 to 71-1408; 73-1674 to 73-1675; 75-0556 to 75-0560; 76-1604 to 76-1607; 77-0351 to 77-0356; 78-0576 to 78-0578; 79-0001 to 79-0003 E-3C: Nine E-3Cs were ordered between 1980 and 1983, equipped for maritime as well as overland operations. · 80-0137 to 80-0139; 81-0004 to 81-0005; 82-0006 to 82-0007; 83-0008 to 83-0009 Conversion designations E-3B: All 25 of the E-3As were upgraded to E-3B standard with the addition of equipment to enable them to operate in the maritime role. · 71-1407 to 71-1408; 73-1674 to 73-1675; 75-0556 to 75-0560; 76-1604 to 76-1607; 77-0351 to 77-0356; 78-0576 to 78-0578; 79-0001 to 79-0003 E-3C: The Boeing Company retained for ongoing development the third aircraft, which has been upgraded to E-3C standard. The designation JE-3A has also been reported for this aircraft, although this is probably unofficial. It has since been delivered to the USAF. · 73-1674