In the Yom Kippur War - which saw the first missile battles at sea ever fought - Israel's missile boats eluded all 54 missiles fired at them, which is what makes so grating the hit suffered by Israel's most advanced missile boat off Lebanon's coast Friday night. Unlike the Katyushas and other rockets being fired from Lebanon or Gaza, the missiles fired at the Israeli vessels, then and now, were homing devices with built-in radar which pursue moving targets once they lock on. When Israel devised its missile boats in the 1960s - the first in the West - together with the Gabriel missile, it did not have to worry about eluding such projectiles since no other country had them. However, it soon learned that the Soviet Union was developing its own missile boats which would be distributed to Arab allies. Israeli naval scientists began thinking about how to deal with the Soviets' Styx missile which had twice the range of the Gabriel. The effectiveness of the Styx was demonstrated in October 1967 when a missile boat supplied by the Soviets to Egypt emerged from Port Said and sank the Israeli flagship Eilat, a destroyer many times its size, with a barrage of missiles. A brilliant naval electronics officer, Herut Tsemach, was assigned the task of devising a shield against the Styx. Without access to the missile itself, he tried to imagine what kind of electronics his counterpart in Soviet naval headquarters in Leningrad had put into the Styx. He then sketched out a proposal for jamming or deceiving the Styx radar. It included an electronic countermeasures system that provided information on the enemy missile's wavelength and pulse rate. Similar emissions would then be sent towards the enemy radar to drown it out or divert it in the pursuit of electronic ghosts. In addition, Tsemach proposed a system for firing chaff, strips of aluminum that confuse enemy radars by reflecting their beams back at them. Since the Styx had twice the range of the Gabriel, the Israeli boats were vulnerable to the Russian missile for 20 to 30 minutes before they could close to the Gabriel's firing range so that enemy boats always got in the first salvos. At least eight Egyptian and Syrian missile boats were sunk in these engagements without an Israeli loss. Naval officials explained Saturday that intelligence had not known that the missile which struck the vessel off Lebanon Friday, a sophisticated Chinese-made weapon upgraded by Iran, had reached Hizbullah's hands. Therefore the devices aboard the missile boat had not been adjusted to deal with the missile's electronic parameters. The writer is author of The Boats of Cherbourg (U.S. Naval Institute Press), an account of Israel's development of the first missile boats in the West.