In a scene reminiscent of the Cold War movie Top Gun, this week a Russian military pilot filmed an American aircraft from his cockpit while both were flying over Syria.
Video of the close encounter was released by Moscow and quickly appeared on social media. And while, unlike Tom Cruise, the Russian pilot did not offer an offensive salutation, there did appear to be a message of defiance - the airspace over Syria is not controlled by the US.
On the same day that video appeared, America and Russia reached an agreement to avoid what the Pentagon calls "any miscalculation and misunderstanding".
But Moscow was less keen to reveal the details of this "memorandum of understanding". The agreement is not a sign of military co-operation but an effort to avoid a mid-air collision.
There have been several incidents of Russian military aircraft coming within several hundred feet of US military aircraft.
They have all been monitored from the ground at the US Combined Air Operations Centre (CAOC) in Qatar. It's the nerve centre from which the US-led coalition is co-ordinating the air campaign against the group known as Islamic State (IS).
Given the security surrounding the base, media access is limited. But the US commander in charge of the air operation was able to speak to the BBC by videolink.
Lt Gen CQ Brown said his forces were "mindful" of the Russian presence, but did not view them as "hostile". He described Moscow's recent intervention in Syria as "an additional wrinkle".
"I do not think the Russians want to get into a conflict with us and neither do we [with them]," he said.
As an aside, Gen Brown also told us he would welcome a decision by Britain to join the air strikes in Syria.
He said the ability to strike in Syria and Iraq gave the coalition more flexibility in putting pressure on IS: "I would welcome anyone, any member of our coalition who would like to strike in Syria, including the UK."
Canada has now pulled out of the fight.
While US commanders play down the dangers of the Russian intervention, others appear more worried.
Attention on Turkey
Nato has its own CAOCs to monitor what's going on in the skies above Europe - one in Germany looks out to the north and east; the other, in Spain, protects the alliance's southern borders.
The BBC was given rare access to the southern CAOC, at a military base on the outskirts of Madrid.
For a short time we were allowed in the operations centre. Officers from Nato nations sit in front of banks of computers - classified information removed before our arrival.
A massive screen in front had deliberately been blurred. But you could still make out hundreds of dots on a map from the Azores to the west and Turkey to the south. Each dot was either a civilian or military aircraft.
From here they've already seen an increase in Russian military activity over the Black Sea. Now their attention's turned to Turkey.
The CAOC commander, Spain's Maj Gen Ruben Garcia Servert, nods rather nervously when I ask him to confirm whether they've witnessed Russian aircraft straying into Turkish airspace.
While he can raise the alarm, and if necessary scramble jets, it's normally left to a member state to decide the course of action. It's not hard to imagine how Nato could be dragged into a wider conflict.
Nato at war
1995: Nato launches its first-ever military operation, carrying out air strikes against Bosnian Serb forces; it later deploys thousands of troops to monitor and enforce a ceasefire in Bosnia.
2003: Nato takes control of the International Security Assistance Force (Isaf) in Afghanistan, its first major operation outside Europe.
2011: UN Security Council approves no-fly zone over Libya to protect civilians from Col Gaddafi's forces; Nato is handed responsibility for enforcement.
2015: Nato renews assurances to defend allies, such as Turkey, in light of Russia's military intervention in Syria.
Gen Servert describes the current situation on Nato's borders as "uncomfortable".
But nearby, Nato is sharpening its military skills to deal with threats that include a more aggressive Russia.
Exercise "Trident Juncture" is Nato's largest war games for more than a decade.
It involves 36,000 military personnel, 3,000 of them British, on land, at sea and in the air across three countries - Spain, Italy and Portugal.
Nato Deputy Secretary General Alexander Vershbow insists it's aimed at dealing with a range of threats and not one particular country.
But the former US ambassador to Moscow says he hopes Russia is taking notice. "We want to deter Russia from even thinking of messing with us," he says. "I hope the Russians draw some appropriate conclusions."
But while Nato is honing its military skills on training ranges and uncontested areas of sky and sea, Russia's armed forces are already engaged in real conflict.
Ambassador Vershbow acknowledges that President Vladimir Putin has changed the post-Cold War order.
He says any notion or hope that Russia will be part of Europe has been "put on the backburner".