EQUIPMENT UPGRADING

As of mid-1968, the 460th TRW had 47 EC-47N/P aircraft assigned. The EC-47N was powered by the Pratt and Whitney R-1830-90 engine; the EC-47P caried the same firm's R-1830-92, the only difference between the two being the accessory package. Both developed approximately 1,100 BHP (brake horsepower) on takeoff. The EC-47Q, not in-theater at that time, was powered by the PW R-2000-4 engine, developing closer to 1,350 BHP, a significant improvement in flight safety for the increasingly heavily loaded aircraft.

Of the 47 assigned aircraft, 30 were "CC" (Combat Cross)-configured--basically ARDF only--using the AN/ALR-34 system with "X" ALR-34 operator consoles, and "Y" acquisition operator consoles. Twelve were "CCZ"-configured, with the ALR-34, the "Y", and two "Zulu" COMINT acquisition consoles to provide extensive intelligence- gathering facilities. The CCZ aircraft were capable of both ARDF and COMINT collection. Five of the EC-47's had a configuration which consisted of the ALR-34, the "Y" console, and two "Q" consoles. The "Q" console had both acquisition and enemy communications disruption (jamming or spoofing of HF) capability. These aircraft were designated "CCQ."

As of midsummer 1970, TEWS-assigned aircraft had reached 55, of which 18 were CC, the remainder being capable of accepting "Z" consoles. The five aircraft with "Q" consoles were still carried on the board as CCQs, but in the interest of weight reduction and mission priority, the "Q" consoles had been removed, with the understanding that they coudl be replaced within 48 hours should a threatening situation indicate the need for communications disruption. (See Figure 2 and Figure 3 for cutout diagrams of CC and CCZ configurations.)

THE ALR-34

The ALR-34 ARDF equipment was an extremely sensitive radio reciver designed to intercept signals from weak trnasmitters emmitting in a power range of 0.5 to 10 watts or more over a frequency spectrum of two to sixteen mhz (A megahertz is equal to one million cycles per second) and designed to allow the operator-navigator team to determine an accurate bearing to the target over a large range of operational variables. The basic inputs to the system were aircraft heading information, aircraft position information, and phase angle-discriminated signals from the antenna system. The imputs were measured and processed in the ALR-34 operator (X) console, then consolidated and relayed to the navigator by a printout from the Franklin Data Printer. The tape printout gave the navigator several items of information such as aircraft position along course (ALC), aircraft position across course (ACC), magnetic heading, time of day to the nearest second, signal strength, attenuation, and raw relative bearing. From this information the namigator manually plotted a line of position (LOP) to the target.

This was the basic ARDF equipment in CC aircraft in 1968, and two years later the same gear was to be found in 20 of these assigned aircraft; while it was still, in 1970, also installed in 15 of the CCZ aircraft.

The basic drawback to the system was that the navigator nad to plot the relative bearings to his captive target manually, on the basis of this magnetic course, evaluate them for accuracy, then convert to true bearing. Other limitations to the system were its limited standoff range, generall 20 miles (the greatest accuracy was at five to ten miles), and its relatively narrow frequency spectrum.