Inside North Korea's mysterious military

Much of North Korea -- and its armed forces -- has been a mystery to the world since it was formed in 1948. But it's not all secret. Because of the country's penchant for holding military parades and firing test missiles, we've been able to gather a lot of information about the increasingly aggressive nation and its capacity for war.

Here's what we know about North Korea, its military, and its worrisome nuclear program.

There are plenty of heavy machines in the North Korean military. According to a Newsweek analysis, North Korea has 3,500 tanks, 72 submarines, 302 helicopters, 563 combat aircraft and 21,100 pieces of artillery.

North Korea's missiles are often used as an expensive show of the country's military strength. Here, a Hwasong-type missile is rolled through the streets of Pyongyang during an April military parade.

Amnesty International estimates that North Korea is spending up to 22 percent of its gross domestic product on its military. (North Korea state media puts the figure at 15.8 percent.) 

One of North Korea's most formidable assets may be the sheer size of its military. Because the country has universal conscription, North Korea's military has 1.19 million active members and another 7.7 million in reserve.

Here, the Korean People's Army marches through Kim Il-Sung square in Pyongyang on April 15, 2017.

The tanks and troop transports seen in parades such as these represent a motorized world far beyond the reach of most North Koreans. Only military and government officials are allowed to own motor vehicles.

This is the Hwasong-15, North Korea's most powerful intercontinental ballistic missile (ICBM). Calculations show the missile has a range of 8,100 kilometers (5,033 miles) with a dummy warhead, but missile experts say a fully armed version would be too heavy to fly that far.

On November 29, 2017, CBS News, citing Pentagon Spokesman Robert Manning, reported that North Korea had conducted a test launch of the Hwasong-15: "The missile was launched from Sain Ni, North Korea, and traveled around 1,000 kilometers (620 miles), before landing in the Sea of Japan."

To celebrate the launch and its self-declared "nuclear statehood," North Korea held a celebratory military rally on December 1 in Pyongyang, complete with fireworks.

The United States and South Korea, meanwhile, responded with a "massive combined aerial exercise" that simulated land strikes.

"Through the drill, the South Korean and U.S. air forces displayed the allies' strong intent and ability to punish North Korea when threatened by nuclear weapons and missiles," a military statement read.

North Korea is working on deadlier payloads as well.

Air Force General John E. Hyten, commander of Strategic Command, told reporters that North Korea conducted a test of a hydrogen bomb (such as the one purportedly shown here by the North Korea state media) on September 3, 2017. The bomb, according to U.S. Secretary of Defense Jim Mattis, delivered an explosion size of more than 100 kilotons.

South Korea, meanwhile, responded to the North's hydrogen bomb test by flying F-15 jets and conducting missile tests of its own on September 4, 2017. The country also announced the rollout of four additional Terminal High Altitude Area Defense (THAAD) missile defense launchers.

THAAD, initially rolled out in South Korea in March 2017, is designed to protect the country against the short- and medium-range missiles in the North's arsenal.

Here, trucks unload the THAAD at Osan Air Base in Pyeongtaek, South Korea.

The THAAD missile defense system does not use explosive warheads, instead relying on kinetic energy to destroy incoming missiles. That is, its guided missiles just smash into their targets instead of detonating. It was developed, in part, as a defense against the Scud missiles launched by Iraq during the Gulf War in 1991.

The successful system was first deployed by the U.S. military in 2008.

THAAD isn't without controversy. Both Russia and China have major concerns over the system, as it would reduce the effectiveness of their own weapons in the region.

Here, residents of Seongju county participate in a protest against aTHAAD system nearby, on March 18. The locals object to the radiation emitted by THAAD's system's powerful radar, VOA News reports.

Of course, the Hwasong-15 is far from the only North Korean missile launched in 2017.

A day after threatening to "sink" Japan and turn the U.S. to "ashes and darkness," on September 15, 2017 North Korea fired a Hwasong-12 test missile directly over the island of Hokkaido, Japan. The missile traveled roughly 2,300 miles during its 19-minute flight.

North Korea also fired a Hwasong-12 missile over Japan on August 29, 2017, seen here in a photo taken by North Korean state media. The launch happened after a series of failed tests on August 25, where two missiles suffered critical flight failures and one exploded on launch.

Kim Jong-Un inspects one of North Korea's Hwasong-12 rockets up close.

And on July 4, 2017, North Korea conducted a test launch of its Hwasong-14 intercontinental ballistic missile. It flew for approximately 40 minutes before landing in the Sea of Japan.

Though North Korea claims its new weapon can strike "anywhere in the world," the United States Department of Defense says the missile has a theoretical range of roughly 3,400 miles -- barely enough to reach the western coast of Alaska.

North Korean dictator Kim Jong-Un, seen here monitoring the July 4, 2017 ICBM launch from an undisclosed location, called the new missile a "gift" to "American bastards."

The United States and South Korea responded to North Korea's ICBM test with a joint missile exercise off the coast of South Korea.

South Korean President Moon Jae-in's office has said the drill was meant to show North Korea a "firm combined missile response posture."

This picture released by the KCNA May 22 purportedly shows a Pukguksong-2 during its test-fire.

This particular missile represents a real advance in tech. It uses solid fuel, which, unlike the liquid fuel used in the past, allows operators to ready the missile while in hiding.

Kim Jong-Un celebrates the test of the medium-range Pukguksong-2 missile May 22. The launch marked North Korea's 10th such test of the year.

U.S. Secretary of State Rex Tillerson said, "The ongoing testing is disappointing, disturbing, and we ask that they cease that," Reuters reported.

Missile launches are a major event in North Korea. Here, a group of North Koreans watch a missile test on a big screen in central Pyongyang.

On November 20, 2017, President Trump responded to the continued tests by designating North Korea a state sponsor of terrorism, noting, "It should have happened a long time ago."

This is the second time North Korea was put on the list. It was first declared a state sponsor of terrorism following the 1987 bombing of Korean Air Flight 858. North Korea was delisted in 2008 as part of an anti-nuclear deal.

Though the Korean War ended with a 1953 armistice, but there was no formal treaty. As such, tensions between North Korea and U.S.-fortified South Korea have remained high.

Today, the two countries are divided by a 160-mile-long, 2.5-mile-wide strip of land known as the Demilitarized Zone (DMZ) that is free of heavy weaponry. The Associated Press reports that North Korea keeps an estimated 60 percent of its forces adjacent to the line.

The North Korean military does not tolerate defectors: In November 2017, a North Korean soldier made a desperate dash across the Korean DMZ.

The soldier, who was shot at least five times, was treated in South Korea for "dozens" of parasitic worms, tuberculosis and hepatitis B, CBS News reports.

South Korea has discovered four tunnels under the DMZ -- apparent attempts by North Korea to create an invasion route. The first tunnel, discovered in 1974, had already been fortified with concrete, wired with electricity and equipped with a narrow railway capable of transferring 20,000 soldiers per hour.

Today, these "tunnels of aggression" are guarded by the South Korean military and are available for visit by tourists.

Tensions at the DMZ are still palpable. Both sides have blasted propaganda at the other through massive outdoor loudspeakers, and episodes of armed violence have erupted.

Here, U.S. Vice President Mike Pence visits Observation Post Ouellette on April 17, a day after a failed North Korean missile test.

Though the U.S. has little to fear from North Korean missile attacks, the South Korean capitol of Seoul is just 35 miles from the DMZ. The U.S. has pledged assistance through missile defenses.

Here, South Korean farmer In-Suk Hwang stands next to the DMZ fence on the island of Gyodong.

Families in North Korea are forbidden from contacting their kin in South Korea. Still, during the annual week-long Chusok harvest festival, families perform ceremonial offerings to their relatives in the North.

Here, the North Korean People's Army stages a combined fire demonstrationon the eastern front on April 26, to celebrate the country's 85th anniversary.

Though the explosive fire power of North Korea's weapons registers well on camera here, few believe the country could actually win a war against South Korea or the U.S. 

"It's just, how much damage can [Kim Jong-Un] do before we take him out?" retired Air Force Gen. Herbert Carlisle told Military Times.

There are more than 25 million people in the Seoul metro area alone. Any war between the North and South would likely start a humanitarian crisis. And should North Korean troops press into the South Korean capital, America's ability to provide air cover would be limited.

Even worse: It's estimated that North Korea has anywhere between 2,500 and 5,000 tons of chemical weapons.

North Korea's unconventional methods of warfare would likely extend to the internet. The UN is investigating a May 8 cyberattack against its 1718 Committee, which investigates violations of the economic sanctions currently levied against North Korea.

The hackers allegedly had "very detailed insight" into the committee and its investigations, Reuters reports. North Korea is also suspected to be behind the WannaCry ransomware attack.