MISSILE THREAT TO U.S. PILOTS

American pilots are finding the skies of N Vietnam more inhospitable than ever before as they drop their deadly cargoes in accordance with President Nixon's instructions.

It's no longer simply a question of 'zapping the Cong'—a favourite sport of the gung-ho US flyers four or five years ago. • Two weeks ago, Washington learnt to its consternation that one of its EB-66 'Pathfinder' planes had been shot down over the N by a surface-to-air missile. It was very bad news indeed for the US Air Force.

The EB-66 is no ordinary plane. It bristles with a formidable array of advanced electronic counter-measure (ECM) equipment and its purpose is to smother the N Vietnamese air defences so that fighter-bombers can reach their targets.

'You should never lose an ECM aircraft to a SAM, one former US pilot told 'Newsweek' magazine. 'Not if it's doing its job. This EB-66 was doing its job and still a good sign.' Newsweek' adds that 'the mounting threat from communist air defences in N and S Vietnam and Laos is causing US air officers serious concern'.

They have good reason to be worried. The N Vietnamese have mastered the evasion tactics used against their SAM missiles by US fighter planes to such effect that they now deal with them "like beaters flushing wild game from the underbrush'.

To evade the SAMs, the US pilots go into a diving turn, the 'split S manoeuvre, levelling off several thousand feet below their original altitude. When they come out of the dive, they find N Vietnam's anti-aircratt gunners have put up a wall of deadly flak to meet them.

Against radar jamming. from the American ECM planes, the Vietnamese use sophisticated tactics-switching on the radar apparatus just long enough to spot their target and sending up their missiles before the plane has had a chance to jam radar.

Worse still, from the US standAbove : Antl-aircraft gun which, with the SAM missiles, is troubling American pilots point, is the use of optical tracking linked to the missiles. "This device,' 'Newsweek' says, comparable to the telescopic sights of a rifle: the operator lines up the cross-hairs of the tracker on an approaching US jet and then simply follows it.

'Any up-and-down or side-toside movements he must make to stay with the aircraft are fed into the SAM system's computer and are converted into guidance directions for the missile. The optical device isn't quite as accurate as a radar, but it is accurate enough-and, unlike radar, it has the advantage of being invulnerable to jamming.' Not surprisingly, US losses in the air over N Vietnam are believed to be much higher than last year. 'Newsweek' quotes one outraged US offiecr as saying: 'We're supposed to be fighting a primitive enemy. But the way things are going that just isn't so any more?