PAPA AIR BASE, Hungary — Hold that convoy right there, general. Can we see your passport, please?

European leaders have made a priority of greater military cooperation, yet the ability of NATO forces to operate in Europe is still hindered by border restrictions and mismatched infrastructure, according to uniformed commanders and EU defense ministers.

While NATO has made substantial progress in surmounting legal hurdles to cross-border operations, lingering bureaucratic requirements — such as passport checks at some border crossings and infrastructure problems, like roads and bridges that can't accommodate large military vehicles — could slow or even cripple any allied response to an emerging threat, officials warned.

To lift the roadblocks, and speed coordinated military action, the Dutch defense minister, Jeanine Hennis-Plasschaert, called on EU officials to create a so-called military Schengen zone. The idea, loosely modeled on the open-border travel zone that has covered most of Europe since 1996, has also been a long-time goal of the senior United States Army commander in Europe, Lieutenant General Ben Hodges.

"We must be able to move quickly to any place where there is a threat" — Dutch Defense Minister Jeanine Hennis-Plasschaert

"We must be able to move quickly to any place where there is a threat," Hennis-Plasschaert said in a statement announcing her proposal at a meeting of NATO defense ministers in June.

NATO leaders insist they have addressed the most problematic obstacles to cross-border operations, but nonetheless welcomed the Dutch proposal as a way to raise political pressure and create a sense of urgency around further improving the "interoperability" of allied countries.

Officials say the obstacles are only apparent during peacetime exercises and planning, and that during a real military emergency, NATO's supreme allied commander for Europe — based in Mons, Belgium — would simply warn allies and deploy as needed.

But officials also said NATO's deterrence mission requires the alliance to constantly demonstrate its capabilities in peacetime and those capabilities are still encumbered. Moving U.S. forces to Poland from Germany, for example, requires a five-day notice period, American officials said.

And then there are infrastructure challenges: roads and bridges that potentially cannot bear the weight of heavy equipment; tunnels that are not tall enough; air strips that cannot accommodate all aircraft.

Win-win

EU leaders at their June summit formally approved a plan for greater military cooperation but the first concrete proposals will not be announced until European Commission President Jean-Claude Juncker's State of the Union speech in September.

According to some officials, the military Schengen zone would be an ideal first step because there is little financial cost or basis for political disagreement.

One historic challenge is that while NATO has greater responsibility for multilateral military cooperation, the EU and its national governments retain authority over border regulations.

Hennis-Plasschaert, in putting forward her proposal, urged NATO Secretary-General Jens Stoltenberg and the EU's foreign policy chief, Federica Mogherini, to work together to overcome such barriers.

A NATO official said that the alliance supported the Dutch proposal, especially if it prompted the EU to take similar steps.

"Overall, we are in a healthy position in terms of rapid deployment in peacetime," the official said. "Efforts in the European Union to improve the cross-border movement of forces and equipment in Europe could also benefit NATO, provided that they are inclusive and complementary to NATO’s work.”

The Dutch proposal called on EU and NATO officials to work out the details, but it's clear that copying Schengen in a literal sense is not the goal, given that not all EU countries are NATO members and not all Schengen countries belong to the EU or the alliance.

"It is important to coordinate military transport in Europe, to ensure that units and equipment are in the right place at the right time, regardless of whether they are deployed in an EU or NATO context," Hennis-Plasschaert said.

A spokesman for the European Defense Agency, which helps coordinate military cooperation among EU countries, said a new joint effort with the European Commission to smooth military transport was expected to begin next month.

Waiting for takeoff

Hodges, a three-star general who is due to complete his tour in September, knows the limitations on military movement firsthand.

Last month, he sat in his jet on the tarmac of Papa Air base in Hungary, engines screaming in the 40-degree heat, as an aide collected the passports of the general and his entourage, including a German military attaché and this reporter, and brought them to be checked by Hungarian border guards waiting in a nearby car, so that the entourage could fly on to a base in Bulgaria.

“Actually, I wish that we could move across Europe as quickly as migrants do” — United States Army commander in Europe Lieutenant General Ben Hodges

Elsewhere on the base, 452 U.S.-led paratroopers were readying their gear to simulate an airborne operation aimed at repelling an enemy force that had occupied the territory of a NATO ally. Hours later, Hodges watched through binoculars as the paratroopers carried out their drill in Bulgaria.

At another point, during related exercises, Hodges was told that his Black Hawk helicopter would have to divert from its intended route in order to clear customs in Romania. Ultimately, Hodges was able to avoid the stop.

While such passport and customs checks are typically routine and not hugely time-consuming, for Hodges they symbolize a tangle of bureaucracy that poses a risk to military speed and efficiency. In Hungary, Prime Minister Viktor Orbán has put up fences to block the flow of migrants, but Hodges said that across much of Europe travel is easier for migrants than for allied military.

“Actually, I wish that we could move across Europe as quickly as migrants do,” Hodges said.

“Of course, we should have to meet all the EU road laws, respect sovereignty, but it is a surprisingly cumbersome process in several countries to get permissions to move troops, weapons, ammunition, even just regular convoys,” Hodges said.

“I was naïve,” the general said, “I just assumed, well, these are all EU countries, or NATO countries, it should be like going from Florida to Virginia on I-95. And it’s absolutely not the case. So there’s just a variety of reasons in terms of diplomatic clearances, regulatory procedures, infrastructure."

Hodges said that investments in military transport and infrastructure also provide a convenient way for NATO allies such as Germany to meet their pledge to increase defense spending in ways that would indisputably benefit the alliance as a whole.