Eyes in the Sky

Measuring the flow of North Vietnamese men and materiel into South Viet Nam is no easy task. The most telling evidence arrives at the Pentagon and the White House in the form of sharp, 9-in.-square photographs ferried by Air Force courier planes from Asia each day. The pictures, showing Ho's men on the move, are the product of the most sustained, highly sophisticated aerial surveillance in military history.

Day in, day out, U.S. photo jets streak over North Viet Nam and Laos, filming huge patches-- and tiny pockets-- of jungled land, searching for the scantest signs of activity by Communist forces. Finding the infiltrating enemy has been a lot easier of late. "We are spotting convoys of more than 100 vehicles in Laos and the lower panhandle now," says one U.S. reconnaissance pilot. "It used to be that 10 to 15 trucks were a big catch." Now nearly every photo foray turns up new roads and fuel depots, fresh truck parks and antiaircraft gun sites.

Since President Johnson restricted bombing to the area south of the 19th parallel, surveillance missions above the line have been flown by the successor to the U2, the supersecret SR-71, double-delta-winged, 2,000-m.p.h. manned missile. Boring ahead faster than a rifle bullet, it takes pictures of astonishing clarity from as high as 80,000 feet. Over the panhandle and Laos, most of the monitoring is the task of the 432nd Tactical Reconnaissance Wing flying out of Udorn in northern Thailand. Its droop-nosed RF-4C Phantoms, unarmed and unescorted, shoot up to a cumulative seven miles of film on the 40 to 50 sorties that the 432nd flies each day.

Suspicious Ladder. Each Phantom carries anywhere from three to nine cameras, including infra-red equipment, as well as side-looking radar, all linked to the aircraft's navigational gear in order to record precise locations--and trip the camera shutters at just the right millisecond. On return to Udorn, automatic machines swiftly process the film in trailers set up beside the runway, and highly skilled (and suspicious) photo interpreters, or PIs, scan it for hours, looking for the smallest telltale detail: a ladder left at a cave entrance, a small dot of light that might be a campfire, vehicle tracks around a supposedly downed bridge. "It's all a battle of wits between us and Ho's people," says an officer.

It is also dangerous business. The pilots of the 432nd wryly refer to themselves as "conscientious objectors who like airplanes and photography," but their war is as risky as any other airman's in Viet Nam. Over the past year, the wing has lost the equivalent of a squadron -- 20 Phantoms. One crew out of seven can expect to be shot down during its tour of duty, for recon missions, unlike the swift, darting thrusts of fighter-bomber strikes, often require four to five minutes of straight and level cruising at low altitude.

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