Nuclear-armed North Korea today marked a military anniversary with a massive conventional firing drill, Seoul said, as a US guided-missile submarine docked in South Korea amid tensions over Pyongyang's weapons ambitions. Speculation had mounted that the North Korea could carry out a sixth nuclear test or another missile launch to mark 85 years since the founding of its army. But no such event - which usually happens in the morning - had taken place by mid-afternoon, and instead Seoul's defence ministry said Pyongyang was conducting a "massive fire drill" in the eastern port city of Wonsan. The South's Yonhap news agency cited a government source as saying the exercise was the North's "largest ever" and presumed to have been overseen by leader Kim Jong-Un. Washington has sent the aircraft carrier USS Carl Vinson to the Korean peninsula, where it is expected to arrive - after a derision-provoking delay - later this week. Confusion had clouded the carrier's whereabouts earlier this month after US officials indicated it was sailing towards North Korea when in fact it was heading south. The vessel will take part in joint naval drills with the South's forces to "demonstrate Seoul and Washington's strong determination to punish North Korean provocations", the South Korean Navy said in a statement. They will take place in the East Sea, the South's name for the Sea of Japan, it said, and the two allies will also begin joint naval exercises in the West Sea - what it calls the Yellow Sea - on Tuesday "in relation to the current security situation". The nuclear-powered US submarine USS Michigan also made a port call at Busan in the South on Tuesday in another show of force. You might also want to see this: President Donald Trump has said the US was sending an "armada" to the Korean peninsula, including submarines. According to the US Navy's Submarine Force Pacific website, the USS Michigan carries more than 150 Tomahawk cruise missiles. They are capable of precision strikes against the North's nuclear facilities, but the South Korean Navy called the visit 'routine' and said the submarine would not take part in any joint exercises. North Korea has ambitions to build a nuclear-tipped missile capable of reaching the US mainland. Tensions have soared in recent months as it carried out a string of missile tests that sparked tit-for-tat sabre-rattling between it and Washington. Pyongyang's rhetoric always intensifies in the spring, when Seoul and Washington hold joint military drills which it sees as rehearsals for an invasion. The North's Rodong Sinmun - the official mouthpiece of the ruling Workers' Party of Korea - warned Tuesday of dire consequences in the event of a US-led pre-emptive strike.