(CNN) -- Six months and more than 17,000 air sorties after it began, NATO's Operation Unified Protector in the skies over Libya grinds on.
What was envisaged in March as a rapid engagement to prevent Moammar Gadhafi's forces from razing Benghazi to the ground has evolved into a long slog. And increasingly NATO operations have dovetailed with those of the rebels -- with the aim of making pro-Gadhafi forces incapable of offensive action.
The initial mandate set out by the United Nations Security Council resolution 1973 was to protect civilians under threat or attack, to enforce an arms embargo on the country and implement a no-fly zone.
"What was initially supposed to be a neutral intervention to protect civilians that were threatened specifically in Benghazi has morphed into being largely a one-sided affair to support the Libyan rebel force to overthrow Gadhafi," says Micah Zenko of the Council on Foreign Relations.
Throughout the conflict NATO has continued to insist that all its actions are aimed at protecting civilians from pro-Gadhafi forces, and that it has not "taken sides." On Thursday, the Royal Air Force spoke of "precision strikes on former regime facilities at Sabratah [west of Tripoli], including a commando base which had been used by Colonel Gadhafi's men to launch numerous reprisals against the local people."
See a timeline of the conflict
But such missions are invariably close to areas where the rebels are trying to break through. In recent weeks, sustained NATO strikes around Brega, Misrata and in the western Nafusa mountains have helped tip the military balance in the rebels' favor, to the point that Gadhafi's opponents have become reluctant to enter the fray until air power has softened up the enemy.
Derek Flood, a journalist and analyst with the Jamestown Foundation, has just spent several weeks in western Libya. "I found the rebels had become almost overly dependent on NATO to the point they wouldn't act without NATO actually softening up the targets first."
Most recently, rebel efforts to take the vitally important town of Zawiyah, just 30 miles west of Tripoli, were preceded by several days of NATO sorties. NATO lists about a dozen "key hits" around Zawiyah in the past five days. The Royal Air Force also targeted a boat commandeered by several Libyan soldiers to get out of Zawiyah, but a statement said that "since it was clear from their actions that these troops continued to pose a threat to the local population, the RAF patrol engaged the ship," which was destroyed.
There appears to be growing coordination between NATO and rebel military commanders.
Video footage emerged at the beginning of this month of a column of rebel tanks and pickup trucks, outside the city of Brega in eastern Libya, daubed with orange paint to distinguish them from government forces and ensure they weren't erroneously bombed.
In previous days, NATO planes had hit several pro-regime targets around Brega.
On a fluid battlefield, where military assets are poorly marked and often hidden in civilian areas, NATO needs forward air controllers to help with targeting.
"Western air forces don't bomb without that direct ability to visualize the battlefield, especially when the regime has placed so many of its assets within civilian protected areas," Zenko says.
NATO spokesman Colonel Roland Lavoie was pressed on the issue at a news briefing last month. "NATO does not have direct coordination with opposition forces or rebel forces in Brega," he said. But he added: "We follow the situation through allied information sources that are in the area."
Zenko says such "allied information sources" may be retired special forces soldiers or military contractors. They are said to be in contact with a liaison office in rebel-held Benghazi, which passes on information to the NATO command center in Naples, Italy.
NATO won't comment on such arrangements.
The arms embargo has been liberally interpreted by some, with Qatar and France supplying the rebels with weapons and military advice. Qatar is reported to have supplied the rebels with antitank missiles, flying them into Benghazi. And Derek Flood said he believes Qatar was also getting weapons to the rebels via the Tunisian border. In the western mountains "there was support on the ground from Qatari officials as well as Emirati officials," he said. Tunisian officials deny weapons are crossing their border. Neither Qatar nor the United Arab Emirates have commented on such involvement.
France acknowledged in June that it had air-dropped assault rifles and ammunition to Berber militia groups in the western mountains but said they were to help civilians protect themselves.
At sea, NATO has operated a blockade -- in accordance with U.N. resolutions -- to prevent any resupply of Gadhafi forces. But in one instance in May a Canadian frigate stopped a rebel tugboat carrying howitzer rounds, ammunition and "lots of explosives" from Benghazi to Misrata. NATO commanders allowed the vessel to proceed on the grounds that it was moving from one Libyan port to another.
More recently, there was the murky case of the oil tanker Cartagena, a vessel owned by the Libyan government but stranded at sea with 30,000 tons of gasoline since May. Rebels boarded the ship in international waters and diverted it to Benghazi with NATO permission. The unknown: Did the rebels have help in seizing the ship? It's not the sort of operation they are used to.
NATO's mission has shifted in another way. After hitting more than 3,000 military targets -- from ammunition dumps to tanks to radar and command-and-control facilities -- there are not many more left. So it has turned to the regime's infrastructure. The satellite dishes of Libyan state TV were bombed on the grounds that the broadcaster was being used to "incite violence." The radar at Tripoli airport also was taken out, and the sprawling Gadhafi compound in Tripoli has been targeted several times.
NATO officials say operations will continue for as long as it takes, though how long it takes to do what is an open question. NATO Secretary General Anders Fogh Rasmussen has said repeatedly that the conflict can only end with a political solution, but the outlines of such a solution are far from clear.
Zenko says the goal from early on has been regime change, and the latest tactic is to try to cut off all economic and outside supplies to make it cease functioning.
While the Libyan regime has lost access to much of the country and is losing critical routes to the east, west and south, Derek Flood says it appears to retain control of border crossings in the Sahara desert -- from Algeria, Chad and Niger.
The military balance has tipped in the rebels' favor. Flood says the capture by rebels of the important road junction at Gharyan 80 kilometers south of Tripoli can only further isolate the regime, cutting off fuel supplies from Algeria. Even so, it still controls large tracts of a vast country.
NATO's current mandate in Libya expires at the end of September. Its members may yet be asked to extend it once again.