SEOUL, South Korea (AP) — South Korea, United States (US) and Japanese warships launched their first trilateral anti-submarine drills in five years on Friday, after North Korea renewed missile tests this week in an apparent response to bilateral training by South Korean and US forces.

The North’s recent five missile launches, the first such tests in a month, also came before and after US Vice President Kamala Harris visited South Korea on Thursday and reaffirmed the “ironclad” US commitment to the security of its Asian allies.

The one-day three-nation training off the Korean Peninsula’s east coast is meant to cope with a North Korean push to advance its ability to fire missiles from submarines, according to a South Korean navy statement.

North Korea has been building bigger submarines including a nuclear-powered one and testing sophisticated missiles that can be fired from them in recent years. That’s an alarming development for its rivals because it’s harder to detect underwater-launched missiles in advance.

South Korean officials said last weekend that they had detected signs that North Korea was preparing to test-fire a missile from a submarine.

Friday’s drills involve the nuclear-powered aircraft carrier USS Ronald Reagan as well as US, South Korean and Japanese destroyers, the navy statement said. During the training, the navy ships from the three nations were to search and track a US nuclear-powered submarine posing as a North Korean submarine while exchanging related information, according to media reports.

“We will respond and neutralise any forms of North Korean provocations in an overwhelming and decisive manner,” Captain Cho Chung-ho, commander of South Korean navy troops who took part in the training, was quoted as saying in the statement.

In addition to its submarine-launched missiles, North Korea has also a variety of nuclear-capable missiles that place both the United States and its allies South Korea and Japan within striking distance. This year, North Korea has performed a record number of missile tests as it refuses to resume long-stalled nuclear diplomacy with the United States.

Friday’s training comes as South Korea and Japan are looking to mend ties frayed over history and trade disputes. The two Asian countries together host a total of 80,000 American troops. Earlier this week, Reagan took part in a joint US-South Korean drills near the peninsula, the first such bilateral engagement involving a US aircraft carrier since 2017.

The North’s most recent missile tests happened on Thursday, hours after Harris left South Korea. During her visit to the Demilitarized Zone separating the two Koreas, Harris said: “In the South, we see a thriving democracy. In the North, we see a brutal dictatorship.”