The following is a script from “The New Cold War” which aired on Sept. 25, 2016. David Martin is the correspondent. Mary Walsh and Tadd Lascari, producers.

President Obama’s nuclear strategy states that while the threat of all-out nuclear war is remote the risk of a nuclear attack somewhere in the world has actually increased. When that was written three years ago the risk came from a rogue nation like North Korea. Back then the U.S. and Russia were said to be partners but that was before Russia invaded Crimea, using military force to change the borders of Europe. And before its president, Vladimir Putin, and his generals began talking about nuclear weapons. For generations nuclear weapons have been seen as a last resort to be used only in extreme circumstances. But in this new Cold War the use of a nuclear weapon is not as unlikely to occur as you might think.

Air-launched cruise missiles being loaded onto a long range B-52 bomber at Barksdale Air Force Base in Louisiana.

David Martin: When you see it close up, it’s, it’s even bigger than you think it is.

Richard Clark: It is an impressive machine. About 185,000 pounds empty. But it’s built to carry weapons and gas.

Major General Richard Clark commands all of this country’s nuclear bombers.

David Martin: And these are the weapons?

Richard Clark: Yes sir. These are air-launch cruise missiles. It is the nuclear primary weapon for the B-52.

Clark told us these are training missiles so they are not armed with nuclear warheads.

A B-52 can carry 20 cruise missiles, six under each wing and eight in the bomb bay.

B-52 bomber CBS News

Richard Clark: So this is the rotary launcher. And it holds eight air-launched cruise missiles within the internal bomb bay of the B-52. It’s a tight fit but the way it works is the launcher rotates, allows the weapon to release and send it on its way.

David Martin: It looks like the chamber of a revolver.

Richard Clark: Same idea. Just much bigger bullets.

As the most visible arm of the American nuclear arsenal these bombers are meant to send a message to an international audience.

Richard Clark: We can put this aircraft anywhere we want, anytime we want and both our allies and our adversaries take note.

David Martin: This is basically a nuclear show-and-tell?

Richard Clark: It’s not just a show-and-tell because it will deliver.

Major General Richard Clark CBS News

Within the last two years B-52s have begun sending that message directly to Russia, flying missions not seen since the Cold War. It started after Vladimir Putin changed history by invading an independent country, Ukraine, and seizing its Republic of Crimea.

Phillip Breedlove: The fact that military force would be used to change an internationally recognized border in the central part of Europe that was new.

Now retired, General Phillip Breedlove was the supreme Allied commander in Europe when Russia took over Crimea. The invasion was carried out by so-called little green men – Russian soliders wearing uniforms without insignia – but looming in the background were nuclear weapons.

David Martin: Was there ever any indication that Vladimir Putin was prepared to use his nuclear weapons in any way?

Phillip Breedlove: Vladimir Putin said himself that he would considered raising the alert status of his nuclear force.

David Martin: He had considered it?

Phillip Breedlove: He said it himself.

Putin said he had given an order to his military to be prepared to increase the readiness of his nuclear forces if the U.S. and NATO tried to block his takeover of Crimea. “We were not looking for a fight,” Putin said in this interview. But “we were ready for the worst-case scenario.”

Phillip Breedlove: They see nuclear weapons as a normal extension of a conventional conflict.

David Martin: So to them nuclear war is not unthinkable?

Phillip Breedlove: I think to them the use of nuclear weapons is not unthinkable.

It says so in their military doctrine, signed by Putin in 2014, Russia “…shall reserve the right to use nuclear weapons . . . In the event of aggression . . . When the very existence of the state is in jeopardy.”

Putin has personally directed nuclear exercises which have increased in both size and frequency, according to Breedlove.

David Martin: More threatening?

Phillip Breedlove: Certainly they get your attention.

David Martin: More aggressive?

Phillip Breedlove: Clearly.

And the U.S. responded with more aggressive exercises of its own. One year after Crimea four B-52s flew up over the North Pole and North Sea on an exercise called polar growl the B-52s were unarmed but that little fin on the side of the fuselage identified them as capable of carrying nuclear weapons.

Hans Kristensen: What I plotted here are the two routes for these planes.

Hans Kristensen, director of the nuclear information project at the federation of American scientists, used Google Earth to show us the message that sent Russia.

Hans Kristensen: Each bomber can carry 20 cruise missiles a maximum of them so we’re talking about potentially 80 cruise missiles that could have been launched against targets inside Russia at this particular time.

Using the cruise missiles range of 1500 miles, Kristensen plotted his own hypothetical lines showing how far they could potentially reach into Russia.

David Martin: And the end points of those red lines?

Hans Kristensen: Yes, each of them go to a facility in Russia that could be a potential target for nuclear weapons.

David Martin: The Russians would look at that and see it as a dry run for an attack on targets inside Russia.

Richard Clark: I guess they can draw the conclusions that they need to draw.

David Martin: Eighty cruise missiles in your face.

Richard Clark: It’s a lot of fire power.

David Martin: Was that the message?

Richard Clark: That’s a message for sure.

The last time American nuclear bombers flew a mission like that was during the Cold War.

Richard Clark: This was a significant exercise for us. We’re training the way we might have to fight.

It was an unmistakable warning -- but Rear Admiral Steve Parode says there’s no indication the Russian military has changed its thinking about nuclear weapons.

Steve Parode: Disturbingly, in recent years there have been specific doctrinal and public statements made by other Russian leaders that indicate an evolved willingness to employ nuclear weapons in the course of conflict.

As director of intelligence for the U.S. Strategic Command, Parode spent the last two years gauging Russia’s nuclear intentions.

Steve Parode: I think that they feel that fundamentally the West is sociologically weaker and if they were to use a nuclear weapon in the course of a conflict between say NATO and Russia they might be able to shock the Western powers into de-escalating, freezing the conflict, into calling a cease fire.

David Martin: So they have a belief that they’re just tougher than us?

Steve Parode: Oh, that’s definitely true.

David Martin: And if they have to use nuclear weapons, we can’t, we can’t take it?

Steve Parode: I think that some people might think that.

Parode is not talking about the Armageddon of an all-out nuclear war which neither side could win. But the limited use of a few nuclear weapons which could convince the U.S. to back down.

David Martin: So, how would they shock us into surrender?

Steve Parode: They could strike a European target with a nuclear weapon, maybe an airfield they thought was vital to conflict between NATO and Russia.

David Shlapak: We’re looking at H-Hour. We’re looking at the, the moment before the conflict starts.

David Shlapak of the RAND Corporation directed a series of war games commissioned by the Pentagon in which Russia invaded the Baltic states of Estonia and Latvia -- two of the newer members of NATO and because of their location on the Russian border two of the most vulnerable.

David Shlapak: When the fight starts, the Russians have about 400 to 500 tanks on the battlefield. NATO has none.

The red chips represent Russian forces. The blue and white are NATO.

David Martin: The relative size of the stacks kind of says it all.

David Shlapak: It does, it does. This is not a happy picture for NATO.

As the scenario unfolds, Russian forces in red are storming the capitals of Estonia and Latvia.

David Shlapak: They can get there between a day and a half and two and a half days – 36 to 60 hours.

To retake Estonia and Latvia the U.S. and NATO would have to conduct a major build-up of military forces to drive the Russians out.

David Shlapak: One of the things you would expect Russia to do would be to begin rattling the nuclear sabre very aggressively, to say, “We’re here. This is our territory now. And if you come and try to take it away from us, we will escalate.”

David Martin: Escalate. Use nuclear weapons?

David Shlapak: Use nuclear weapons.

Russia has more than 1,000 short range nuclear weapons while the U.S. has less than 200 at air bases in Europe.

Hans Kristensen: There’s one in Germany…

The locations of American nuclear weapons are officially secret. But here’s what they look like. Hans Kristensen says he discovered this photo on a U.S. Air Force website showing the inside of a shelter where nuclear bombs would be loaded aboard American and NATO jet fighters.

Hans Kristensen: Each vault can have up to four nuclear bombs. They hang right next to each other.

Hans Kristensen: It can - it sinks into the ground with the weapons, levels completely with the surface.

David Martin: And just out of a doomsday movie the nuclear weapon rises out of the floor.

Hans Kristensen: Right.

The bomb is called the B-61 and it’s being upgraded by adding a new set of tail fins that give it greater accuracy. That would allow the B-61 to destroy its target using a lower-yield nuclear weapon which would decrease the number of civilian casualties.

The air-launched cruise missile, says Major General Clark, can also be turned into a low-yield nuclear weapon.

Richard Clark: There is a variable yield option on this weapon, so we can change that yield within the weapon.

David Martin: You can dial in a yield?

Richard Clark: That’s what we call it, actually. Dial a yield.

David Martin: Does that make a nuclear weapon easier to use?

Phillip Breedlove: We do not plan to go there. We do not want to go there.

David Martin: But if you have this option which allows you to keep civilian casualties to a minimum and you’re really up against it, isn’t it easier?

Phillip Breedlove: I don’t think that any decision to ever use a nuclear weapon could be categorized as easy.

David Martin: Less difficult?

Phillip Breedlove: Less difficult. We could say that.

Russia is also developing low-yield weapons which this declassified CIA document says could “…lower the threshold for first use of nuclear weapons...” “the development of low yield warheads that could be used on high-precision weapon systems would be consistent with Russia’s increasing reliance on nuclear weapons…”

But “increasing reliance on nuclear weapons,” says Rear Admiral Parode, doesn’t mean Russia is eager to use them.

Steve Parode: I don’t perceive that they are, have become madmen with their fingers on the button. But I do believe they are more interested in considering how nuclear weapons could be used in conflict to either close a gap or to sustain the opportunity for victory.

David Martin: So what’s the scenario? What situation would get them to seriously consider the use of nuclear weapons?

Steve Parode: That is probably the greatest question I’m trying to answer today for Admiral Haney.

U.S. Strategic Command Center CBS News

That’s Admiral Cecil Haney, head of the U.S. Strategic Command, the man who would carry out a presidential order to launch a nuclear weapon.

Cecil Haney: Thank you. I appreciate the update.

Low key and cerebral, Haney commands not only this country’s nuclear forces but its cyber weapons and space satellites as well.

David Martin: Is it riskier today?

Cecil Haney: Well I think today we’re at a time and place that I don’t think we’ve been to before.

It is Haney’s job to convince Vladimir Putin that resorting to nuclear weapons would be the worst mistake he could possibly make.

David Martin: When you look at what would work to deter Russia, do you have to get inside Putin’s head?

Cecil Haney: You have to have a deep, deep, deep understanding of any adversary you want to deter, including Mr. Putin.

David Martin: So how would you describe him psychologically?

Cecil Haney: Well, one I would say I’m not a psychologist. But I would just say he is clearly an individual that is an opportunist.

David Martin: Does it concern you that an opportunist has a nuclear arsenal?

Cecil Haney: It concerns me that Russia has a lot of nuclear weapons. It concerns me that Russia has behaved badly on the international stage. And it concerns me that we have leadership in Russia, at various levels that would flagrantly talk about the use of a nuclear weapon in this 21st century.