He says he's issuing a "red alert" to the world after a pretty turbulent year.
The vessel may be in violation of U.N. sanctions barring some types of trade with with North Korea.
The U.S. Treasury Department announced sanctions on two North Korean government officials involved in weapons development.
The hearing was partly about President Trump, but also about the changing nature of nuclear threats.
A new report is hoping to keep nuclear security in the international conversation.
The Congressional Budget Office says about $400 billion of that will go toward modernization.
Earlier this month, President Trump said he wouldn't recertify the Iran nuclear deal.
North Korea's deputy ambassador to the U.N. said the situation in his country has "reached the touch-and-go point."
Nations acquire nuclear weapons for all sorts of reasons, and it's rarely about actually setting off the bomb.
The alert was spread via text message and social media to a "handful of service members and families."
The Hermit Kingdom is threatening the U.S. and Japan after the United Nations hit the country with new sanctions.
The U.S. reportedly wants to cut off oil and natural gas exports to North Korea, but China and Russia could veto that plan.