The object of Operation Allied Force was "to attack, disrupt, devastate and ultimately destroy Serb forces" until attacks on civilians ceased and President Milosevic accepted that the ceasefire in Kosovo must be policed.
What was the NATO plan, how has it been disrupted, what has been achieved? Like all big projects, it was broken down into phases. This eases planning and logistics and enables progress to be assessed.
Phase I: The establishment of air supremacy or at least air superiority.
Phase II: If Mr Milosevic remains defiant, air attacks on Serb ground forces.
Phase III: Assuming a ceasefire followed by an agreement, policing that agreement by NATO or other troops.
Phase I is normal in modern operations. It aims at enabling ground troops to manoeuvre and logistics convoys to move without threat of air attack. A complementary aim is to enable NATO air power to operate freely in all phases. So components of the Serbian air defence system - airfields, planes, radar sites, missiles, guidance equipment and communications - were early targets. This took about a month in the Gulf War. But Milosevic struck at NATO's Achilles heel, the Kosovan civilian population, even before the attack started. He subsequently intensified this, with the results we see.
Two factors upset this phase. The bad weather (which was forecast) was more inhibiting than was originally thought or admitted. Secondly, there were not enough aircraft to sustain both the bombing campaign and the low-level air strikes needed to reduce the attacks on civilians.
Gen Sir Charles Guthrie, the Chief of the British Defence Staff, said on Sunday that the RAF had successfully dropped only two bombs in the first four days of Phase I, because bad weather obscured targets. The position was unchanged after the sixth night. Such frankness makes for trust; the tabloids and TV had given a very different impression. The fact is that many high-tech guidance systems are still vulnerable to the ancient military scourge - bad weather.
More aircraft were decided on at the weekend when the decision was quickly made to advance the start of Phase II. Ten US Warthog tankbuster planes are being used. Four B1B bombers carrying a new type of air-burst fragmentation bomb with an all-weather guidance system plus additional British Harriers are also being deployed.
There was some unease over the depleted uranium shells used by the A10s. Some people blamed these for Gulf War illnesses but so far there seems no clear evidence.
The A10s are affected by weather but the B1B bombs, using a GPS system (global positioning by satellite) are said to be unaffected.
So the phases have been telescoped and air superiority has not been established before starting Phase II. The air defences are not destroyed and Serb morale seems high.
The attacks will be from medium rather than from low levels because of the Serb army's 1,850 air defence guns and machineguns, firing 20 mm, 30 mm and 57 mm ammunition. The Serbs also have 60 surface-to-air (SAM) missile launchers, including the SAM 14, the improved shoulderfired SAM 7.
Air defence guns and machineguns were very effective against aircraft flying low in the 1973 Middle East war, if huge amounts of ammunition were available. This would make attacks by the A10 tankbusters rather dangerous.
NATO is nothing if not a vast planning machine and there seems to have been contingency plans called Tier I, Tier II and Tier III. The details are not public but ground troops for Kosovo seem to be included. However, NATO seems to have convinced itself that the new missiles and guided bombs would do the job.
If it is intended to take on the Serbian army in Kosovo, the estimate of at least 80,000 troops seems realistic. How to get them to Albania or Macedonia? That will spoil Easter for the planners!
And the hot potato, who pays? Saudi Arabia, the Gulf States, Germany, Japan and the EU paid for the Gulf War; they will hardly pay for this one. It cannot be a levy on UN members: the Security Council was not consulted. (The General Assembly, because it has representatives from all members must agree to expenditure). Whatever one feels about bombing, some might think it unwise to leave NATO with the whole bill, if only because the alliance might never again take on an aggressive state.
The whole question of intervention in the internal affairs of a state was thrashed out after the Gulf War in the military and diplomatic magazines. The argument has now restarted.