iStock/Thinkstock(NEW YORK) — On Tuesday night, North Korea launched a KN-15 missile from its eastern coast into the Sea of Japan, marking the fourth missile test conducted by the North Korean regime this year alone.

Here’s what to know about each of those tests:

Feb. 12

In February, North Korea successfully tested a land-based version of a KN-11 missile, a solid-fuel rocket, which traveled 310 miles into the Sea of Japan.

Gen. John Hyten, the commander of U.S. Strategic Command, told a congressional panel Tuesday that the February launch marked a significant advancement for North Korea because it was its first successful solid-fueled missile fired from a mobile launcher.

Mobile-launched missiles are harder to track and can be fired at short notice.

Hyten labeled the launch of the KN-11 missile as “a major advancement” by North Korea because it was “a new solid medium range ballistic missile off a new transporter erector launcher.”

The February launch occurred as Japanese Prime Minister Shinzo Abe visited President Donald Trump at his Mar-a-Lago estate in Florida over the weekend.

Photos taken by the club’s patrons and later posted on Facebook captured Japanese and U.S. officials responding in real-time to the incident, sparking criticism about why such important meetings were not conducted in a more secure location.

March 6

In early March, North Korea launched five medium-range Scud-type missiles. Four traveled more than 600 miles, the upper limit of their range, into the Sea of Japan. The fifth took off, but later crashed.

Three missiles landed in waters in Japan’s economic exclusion zone, which extends 200 miles from its shoreline.

Shortly after this test occurred, the U.S. delivered the Terminal High Altitude Area Defense (THAAD) anti-missile system to South Korea, a process which the U.S. started working on with its ally after the flurry of North Korean missile tests in 2016.

THAAD is a missile defense shield designed to intercept short and medium range missiles.

March 21

Later in the month, North Korea tested a mobile-launched missile which exploded “within seconds of launch,” according to U.S. Pacific Command.

The launch was near Kalma in eastern Wonsan province, where North Korea previously attempted to test its mobile-launched Musudan intermediate-range ballistic missile. Last year, North Korea test-fired eight Musudan rockets, but only one was considered a success.

U.S. officials have not identified what type of missile was tested on March 21 since it exploded so soon after launch.

April 4

Tuesday’s KN-15 missile launch comes just days before Chinese President Xi Jinping will meet with President Trump at Mar-a-Lago, during which North Korea is expected to be a major point of discussion.

“Yes, we will talk about North Korea,” Trump told the Financial Times over the weekend. “And China has great influence over North Korea. And China will either decide to help us with North Korea, or they won’t. And if they do, that will be very good for China, and if they don’t it won’t be good for anyone.”

According to the FT, Trump said the U.S. could “totally” handle the situation in North Korea without assistance from the Chinese, but he declined to go into specifics.

U.S. Secretary of State Rex Tillerson released a terse statement following Tuesday’s test, saying, “North Korea launched yet another intermediate range ballistic missile. The United States has spoken enough about North Korea. We have no further comment.”

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