USA: Two of North Korea's most recent weapons tests, both of which involved mock nuclear attacks, have been described in detail. A few hours prior to the arrival of a US warship in South Korea, Seoul also reported that the DPRK launched numerous ballistic missiles into the ocean. Between March 25 and March 27, Pyongyang claimed to have tested its new "nuclear unmanned underwater attack boat," adding that the "test combat unit" had been "accurately detonated underwater." Previously referred to as a secret weapon, North Korea's military has claimed that the platform can "annihilate enemy ship groups" without being noticed and create a "radioactive tsunami" using underwater explosions. Also Read: Several fish perished as a result of a nuclear plant leak in Minnesota. The weapon was submerged for more than 41 hours before it exploded off the coast of North Korea, according to a report published on Tuesday by the state-run Korean Central News Agency (KCNA). Another recent exercise involved the loading of tactical ballistic missiles with "virtual nuclear attack" test warheads that were detonated 500 metres above their intended target in order to test the military's "firing preparations." According to KCNA, the launch unit commander stated that the exercise proved that "if we fight, we will definitely annihilate the enemy." North Korean leader Kim Jong-un emphasised the need to "qualitatively strengthen the DPRK's nuclear forces" during a meeting of the ruling Workers' Party on Monday. He also claimed to have "reviewed the prepared nuclear counterattack operation plan" in the event of a conflict. Also Read: Images of the objects shot down over North America last month have not been made public by the Pentagon The most recent tests occur as tensions between Pyongyang, Washington, and Seoul are at an all-time high. The US has been leading a series of large-scale military exercises in the area in recent months, which the DPRK has repeatedly criticised as a prelude to an attack. North Korea has conducted an unprecedented number of weapons tests in retaliation, including several ICBM tests, drawing criticism from the US. The military of South Korea earlier on Monday claimed to have discovered two short-range ballistic missiles launched from the DPRK's North Hwanghae province. Officials in Tokyo claim that both were launched in the direction of Japan but came to rest outside the nation's exclusive economic zone. The South Korean military issued a statement saying, "We will closely monitor North Korea's various activities and maintain a firm readiness posture based on the capability to overwhelmingly respond to any provocations." Also Read: New Zealand has expressed a desire to sign up for the AUKUS security agreement with the US, UK, and Australia. The military added that it would continue scheduled drills with the US, which sent an aircraft carrier that was scheduled to dock at a South Korean naval base on Tuesday, despite repeated warnings from Pyongyang. Before it arrives, the warship will take part in the most recent of many similar drills alongside South Korean forces in the waters off its east coast.