After the Sun Goes Down

Since using flashers resulted in shot-up airplanes, the RA-5C Vigilante had three sensors which could be used at night: Infrared Mapping (IR), Passive Electronic Counter Measures (PECM), and Side-Looking Radar (SLR). Although these systems could be run while jinking, the best results came from steady, wings-level flying.

Side-Looking Radar was installed in all RC-5Cs, (the rear two-thirds of the belly canoe was antennas, power supplies and recorders for the SLR). In addition to providing intelligence—boats, ships and trains showed up especially well—SLR gave the A-6 Intruder and, later, the A-7 Corsair crews a current radar picture to use in their planning for attacks in bad weather or at night.

The installation of the Infrared (IR) Mapping sensor (designated AAS-21) was a major improvement in the Vigilante’s night capability. No longer would the flashers be the only way to obtain night imagery. The “Double-A,

Ess 21” used liquid nitrogen to cool sensing crystals which detected temperature differences. The system would show dead vegetation used as camouflage, find the hot engines of vehicles in the night and even show patterns of warmth where vehicles or airplanes had been parked. The IR was run on all missions, supplemental in the day and a primary sensor at night.

Early runs with the AAS-21 over the Ho Chi Minh Trail showed hot spots that intelligence officers and photointerpreters could not figure out. The hot spots turned out to be fresh elephant droppings.

Back in Albany, Georgia, while the system was still classified as secret, an unmarked, old Beech 18 airplane arrived at the Navy air station, had the system installed and flew a series of night flights. Speculation ran wild.

The Twin-Beech turned out to be operated by the U.S. Alcohol and Firearms Bureau which was locating illicit whiskey stills in the hills of northern Georgia. Later the Vigis themselves would fly these “revenoo-er” searches.

PECM stood for Passive Electronic Counter Measures although “counter measures” was misleading. PECM (AN/ ALQ-161) was a special installation that in the RA-5C replaced one of the internal fuel cans. A close look at a Vigilante shows square antenna panels scattered along the fuselage sides. However, since the panels are painted the same as the rest of the aircraft, they are usually not noticeable. The inertial navigation system, INS, backed up by the RAN’s log, provided an accurate position of the RA-5C to the PECM. On return to the ship, the magnetic tapes were read and the location of radar and electronic emitters, like tracking and fire control radars, were automatically printed on a map. The PECM also recorded the PRF, band width and other parameters that enabled the intel officers to determine exactly what type and model radar it was. The two primary PECM tracks were north and south along the borders of North Vietnam. The Black Track was over Laos and the Blue Track over the Gulf of Tonkin.

Night PECM missions during the “Highway Patrol” period of the war were usually quiet flights; boring enough that the Vigi pilots would let the autopilot fly the airplane and help the RAN by writing down navigational fixes. All the way north along the border, the ALQ would be quiet with only an occasional beep from search radars. Then at the end of the route near the Mu Gia Pass, as the RA-5C started to turn around, the warning gear would come alive with pulsing strobes on the threat display and ululating warbles in the headphones—every indication of tracking anti-aircraft guns and imminent SAM launch. The crew’s pulse would shoot up and adrenaline would flow as they prepared to evade missiles or flak. Then it would all suddenly stop, just as the wings leveled after 180 degrees of turn. The Vietnamese knew that the information gathered by the PECM was not especially accurate when the aircraft was turning.

Another night on the Black Track over Laos, a crew from RVAH-6 had excitement of another kind. Air Force B-52s were effectively, if inefficiently, carpet-bombing North Vietnamese Army and Viet Cong storage and troop areas in South Vietnam, Cambodia and Laos. Each bomber dropped 84 500-pound and 24 750-pound bombs and the B-52s flew in cells of three. There were 324 bombs with a combined weight of 90 tons from one cell that created utter devastation in mile-wide swaths. The massive bombdrops were called “Arc Light.” As a precaution before bombs away, announcements were made over the radio on guard channel which all friendly aircraft monitored.

Your author was flying blissfully along on a Black

Track when guard channel blared, “Arc Light, Arc Light, coordinates north seventeen twenty-two, east one-ohsix zero-five, Arc Light, Arc Light.” I did not pay much attention; Arc Light warnings came frequently.

Moments later, my backseater, Lt. Cdr. “Bull” Davis, announced on the intercom, “We’re there.” I looked up over my shoulder and there were the black silhouettes of six B-52s. I lit the afterburners, rolled, pulled and dived fast to get out of the way. Safely away, we looked back to see explosion after explosion rippling through the jungle—so close together they formed a solid carpet of flame and fire.