It's all go at NATO headquarters in Brussels.

As the North Atlantic Treaty Organisation prepares to celebrate its 70th anniversary, staff have moved into a massive new facility boasting 18 conference rooms, state-of-the-art sustainability features and 72,000 square metres of glass.

Opening the new HQ, which reportedly cost $US1.23 billion, secretary general Jens Stoltenberg praised his organisation as the "most successful military alliance in history".

But increasingly, questions are being asked about whether NATO is both fit-for-purpose and fit-for-duty — particularly given repeated threats and sabre-rattling from Russian President Vladimir Putin.

Mr Stoltenberg lists NATO's strengths as unity and an "ability to adapt to change" — but they're the very areas where critics suggest NATO needs to lift its game.

So what immediate reforms could the alliance undertake to sharpen its edge? How can you strengthen NATO without increasing tensions with Russia? What role should America play in its future? Four experts weigh in.

Appoint a European as Supreme Allied Commander

Since its creation, NATO's commander has always been an American, starting first with Dwight Eisenhower.

But military historian and former United States colonel Andrew Bacevich argues NATO needs a European as its military leader.

Some experts think America should play a lesser role in NATO, or withdraw altogether. ( Getty Images: The Asahi Shimbun )

He says that would have both "symbolic and substantive" value, encouraging Europe to be less dependent on American leadership and money.

"The most important thing would be for the parliaments in these various countries to make a commitment to expanding the size of their defence budgets," he says.

"They are wealthy countries, they are stable democracies and they can do more to carry the load for their own benefit."

He is also a long-standing advocate of a US withdrawal from NATO — a move originally foreshadowed by Eisenhower in the early 1950s.

"Europeans today are perfectly capable of defending themselves," he says.

Ensure the free flow of troops and equipment

Judy Dempsey says military resources should be able to move more freely around the EU. ( Getty Images: Paul J Richards )

Judy Dempsey, the editor-in-chief of Strategic Europe and a senior fellow with Carnegie Europe, believes the alliance needs to overhaul its logistical capabilities.

She says NATO has fractured over time and she blames it on growing complacency since the end of the Cold War.

She advocates a military equivalent of the Schengen arrangement, which enables the free movement of people across the European Union.

"The institutional framework for moving troops across Western Europe has more or less disintegrated: bridges, places for landing, small airports, the energy grids, railways — you name it," she says.

"The big developments in infrastructure projects to actually transport troops and equipment quickly, have just faded away over the past 25 years."

The end result, she says, has been an erosion of military preparedness, with European members lacking basic logistics.

"We are talking about heavy airlift for equipment and personnel, we're talking about coordination of intelligence gathering, we're talking about so many different systems, whether it be tanks or fighter jets or helicopters," she says.

"You know, there are such different systems, that one pilot cannot sit in the helicopter of another country because they don't share the same equipment.

"These are really basic flaws and they are taking a long time to be remedied."

Reaffirm NATO as a defender of democracy

NATO's membership has expanded and now includes 29 nations. ( Getty Images: John Thys )

Heather Conley sees the biggest threat to NATO's future coming from within.

Ms Conley, from the Centre for Strategic and International Studies in Washington, says as NATO has expanded its members, it has lost political focus and purpose.

She says members like Hungary and Poland, both former members of the pro-Soviet Warsaw Pact, are now sliding increasingly toward authoritarianism.

"I think NATO needs to have very open and honest political conversations about the health of its democracy," she says.

"The community is only as strong as its weakest link. We are now seeing pretty dramatic backsliding. We are looking at some of the most basic elements of rule and law being severely degraded."

She singles out Turkey, a NATO member since 1952, for particular attention.

Heather Conley says Turkey is trying to buy Russian S-400 missile defence systems. ( Getty Images: Sergei Malgavko )

"We have to re-anchor Turkey towards NATO, towards the West. It is being pulled in very different directions," she says.

"This is a country that is increasingly using its military to achieve political objectives without a unified NATO approach.

"We do run the great risk of having US and Turkish forces firing on each other in Syria. We have Turkey contemplating the purchase of Russian S-400 missile defence systems, which would just be anathema to NATO and really impede NATO interoperability."

Abandon long-standing plans for Eastern expansion

At the end of the Cold War, NATO had 16 members. It now has 29.

That expansion saw many former Communist countries come into the fold, including nations that border Russia — Estonia and Latvia.

Strategic analyst Michael O'Hanlon believes that embrace significantly increased tensions between Russia and the West.

And though he in no way defends the aggressive actions of Mr Putin, he argues any further expansion of membership risks making a tense situation worse.

Tensions between Russia and the West are high. ( Getty Images: Mikhail Svetlov )

NATO has previously signalled a willingness to grant membership to Georgia and Ukraine, but Mr O'Hanlon says those plans should be scrapped.

"What I'm worried about is the chance of war between Russia and NATO," he says.

"Our pledge to bring in Ukraine and Georgia … is essentially meaningless because we see no viable path to actually include them. Yet the fact that that pledge is out there gives Putin incentive to keep messing around with these countries' internal security and borders."

He instead offers the idea of creating an "arc of neutrality" — a buffer zone of neutral nations between Russia and the West.

"I'm not presuming that if we do this deal, Russia is going to turn into some meek and supportive lamb — essentially a pro-Western country," he says.

"We've got to expect we still need military deterrence and defence."

He concedes the proposal is speculative and would be near impossible to achieve, given current political tensions and suspicions.

Mr Bacevich agrees: "I think it's an interesting idea … about 15 years too late."

"Before NATO expanded eastward up to the border of Russia, at that point it might have been possible to create this neutral buffer between East and West," he adds.

"But the expansion of NATO is now an accomplished fact and it seems to me that it can't be undone. I think it was probably foolish to do it in the first place, but now it can't be undone."