The U.S. Army reportedly is discussing with Rafael Development Systems whether its Trophy Active system, designed to detect and protect against anti-tank threats, might be adapted for use by helicopters. Eight U.S. helicopters have been shot down in Iraq since Jan. 1, the most recent being a UH-60 Black Hawk downed north of Baghdad Feb. 21. At least one downing is attributed to new weapons in the hands of insurgents (Russian-built SA-14 or SA-16 anti-aircraft missiles). But U.S. officials in Iraq blame most of the eight, including the latest, on a new insurgent tactic of concentrating small-arms and rocket-propelled grenade fire against helicopters on known flight paths.   For related news