It was, presumably, an attempt to assert their claim of sovereignty over an expanse of open sea reaching from their shores most of the way to Italy. To the U.S. Navy, it was a matter of keeping the open seas open. To the Navy pilots, it was a reflexive response to shoot when shot at. Sensible people never take pleasure in seeing these weapons used. There will be, necessarily, much inquiry into the origin of this incident, and whether it might have been avoided. The question is altogether proper, but it may well turn out that, realistically, there was no way to avoid this kind of collision with the world's most utterly reckless government.
The Libyans, under the energetic leadership of Col. Muammar Qaddafi, are running a sort of pirate kingdom that recognizes no law but its own. It is characterized by unbounded ambition, extreme naivete and the inordinate wealth generated by its oil fields. That's an uncomfortable combination, particularly for the countries nearby. Libya's troops have pushed down into its defenseless neighbors in central Africa. The Sudanese have openly called for the overthrow of Col. Qaddafi. His feud with Egypt, which he once tried to invade, has gone on for years. In several European countries, as well as in the United States, the Libyans have been running-- usually through their diplomatic missions--a systematic campaign of assassination of the colonel's enemies. Some of the oil money is being used to buy an immense arsenal of advanced weapons. Some of it is being used to try to develop nuclear weapons. Libyan purposes and practices cut across the basic rules of civilized conduct at so many points that yesterday's exchange of fire is, unfortunately, merely part of a larger pattern.
Further questions: What, precisely, was the Libyans' purpose in sending out the planes? Why use these Soviet planes, inferior to the American fighters, when Libya has better ones? Why, after a number of Libyan planes approached the carrier force and veered off, did one of them choose to fire? Can it be proved that the Libyan fired first? Who, incidentally, was flying those planes? Not many of Libya's jet pilots are Libyans.
A decent respect for international law--on the American side, if not Libya's--requires an earnest effort to extract as many answers, publicly, as possible. But there is no country anywhere that will have less benefit of anybody's doubt than Libya. The single useful purpose that the Qaddafi regime serves is to remind people what the world would be like if there were no law, and no law enforcement, among nations.