As the amphibious assault vehicles storm towards the beach, smoke grenades are fired to provide cover.
In this scenario, the South Korean Marines are about to land in enemy territory. They need all the protection they can get.
After making landfall, the soldiers storm out of the 23-tonne assault vehicles and secure the area.
Their backup, the United States Marines, arrive soon after on a much larger hovercraft known as a landing craft air cushion, packed with additional vehicles, weapons, and supplies.
Just out of sight are some 30 warships and 70 aircraft, including fighter jets and Apache attack helicopters.
March to April is the season of war games on the Korean peninsula and this drill, known as Exercise Ssang Yong or "Twin Dragons", is one of the largest.
It's also one of the more controversial, seen by North Korea as an invasion rehearsal.
It was, after all, a US-led amphibious assault in 1950 that turned the tide of the Korean War, saving South Korea from defeat and securing its very existence.
But the US and South Korea argue their joint training is simply business as usual.
"This is a routine exercise," Captain Kevin Buss, from the US Marines, told reporters on the beach.
"It's defensive in nature. It's just contributing to the combined defence of the Korean peninsula."
Tensions on the Korean peninsula have been escalating over the past 18 months, with North Korea firing more than 100 missiles of varying capabilities — a record for the regime.
However, it's not the number of missiles that worries experts, but rather the regime's expanding capability.
In recent weeks, Pyongyang claimed to have successfully test-fired its first submarine-launched cruise missile, an underwater drone capable of carrying a nuclear warhead, and its "most powerful" intercontinental ballistic missile.
The Hwasong-18, launched last week, is a "solid-fuel" ICBM, which can be moved more easily and fired much quicker than liquid-fuel ones.
North Korea has at least 30 nuclear warheads at the ready, according to the latest report from the Federation of American Scientists.
It's understood these can effectively hit targets within 500 kilometres, but North Korea is fine-tuning the technology to strike targets thousands of kilometres away, including the United States or Australia.
"To the layman, it looks like, 'Oh, North Korea has fired another missile,'" retired South Korean Lieutenant General Chun In-bum said.
"Well, it's different. The type of missiles is different, the range is different.
"The only thing we can say for certain is it's improving day by day. And only God knows where these weapons systems will end up."
The beach landing drill marked a return of large-scale bilateral war games on the Korean peninsula, which had been pushed aside to allow diplomacy with the North in 2019, then later, because of the COVID-19 pandemic.
North Korean leader Kim Jong Un and then-US-president Donald Trump famously met at the demilitarised zone, but failed to produce an agreement after three meetings.
The suspension of field exercises that year meant some "basics" had to be relearned, but the commander of the 13th Marine Expeditionary Unit, Colonel Samuel Meyer, denied a loss of "readiness".
"I don't think we've lost some of our edge. We're just sharpening that again," he said.
The exercises also come as South Korea and the United States marked 70 years of their alliance, a pact that has helped deter North Korea.
"We're here to show how we are capable with our allies," Colonel Meyer said.
"We support stability in the region."
For South Koreans, there are bigger threats on the horizon
Residents in South Korea's capital have had to endure North Korea's threatening behaviour for decades.
It's only a short drive from Seoul to the border, and the city has about 1,000 artillery systems pointed directly at it.
An attack on the capital would be catastrophic, with around two-thirds of the country's wealth contained in the greater Seoul metropolitan region.
But for many residents, the latest posturing from Pyongyang is not a big concern.
"This is what North Korea has always done," one resident said.
"We don't worry much because we believe in our country and our friendship with the United States."
Kim Hyun-tak runs a small business selling outdoor equipment and emergency supplies.
When tensions have escalated in the past, he has noticed a spike in sales. But in recent months, sales are down.
"The economy isn't good at the moment," he said.
"Cost of living is the real problem, rather than the North Korean nuclear threat."
But the North Korean threat is being taken seriously at the highest levels of government.
So much so, South Korea is trying to resolve historical disputes with its former coloniser, Japan, to unite against a common enemy.
North Korea's language has also become more threatening, with Kim Jong Un's sister Kim Yo Jong recently warning of "swift and overwhelming" military action against South Korea and the US.
But retired South Korean Lieutenant General Chun In-bum says a sudden attack from the North is unlikely, despite its threatening language.
"North Korea is smart enough to know if they use nuclear weapons, it'll be the end of them, for now," he said.
"They are not crazy. They have a goal … which is regime survival."
So, where is this all heading?
North Korea is desperate to be recognised as a global nuclear power, something the West is refusing to do.
In response to comments from G7 leaders this week condemning the recent tests, Foreign Minister Choe Son Hui described North Korea's status as a "world-class" nuclear power "final and irreversible".
Pyongyang wants sanctions against it to be lifted, and dreams of a "final victory" where it conquers South Korea and reunifies the peninsula.
And while that may be a pipe dream, Lieutenant General Chun says North Korea represents a destabilising force not just on the Korean peninsula, but for the entire world.
The country was already selling conventional weapons to other rogue regimes, such as Myanmar, Iran, and Russia, he said.
"It only goes to common sense they will probably proliferate their technologies and knowledge of nuclear systems," Lieutenant General Chun said.
A more powerful Pyongyang also amplifies tensions in the Indo-Pacific, which have been elevated due to Russia's invasion of Ukraine and China's assertive actions in the region.
Chinese spy ships often tail the United States Navy in the region, but at the recent Ssang Yong exercises, a Russian "shadow" was also sailing about 15 nautical miles away.
"All interactions were routine and professional. We're sailing as normal," Navy Captain Tony Chavez said.
But China's military build-up in the East and South China Seas, along with threats to invade the self-ruled island of Taiwan, have fuelled concern a conflict is brewing.
China conducted huge military exercises around Taiwan this month after President Tsai Ing-wen met with US House Speaker Kevin McCarthy in Washington.
It followed similar exercises carried out last year after Ms Tsai hosted former speaker Nancy Pelosi.
If war did break out on the Taiwan Strait, there are growing expectations the United States and its allies would be drawn in to defend the island.
It's a war the two Koreas would unlikely be able to sit out on, Lieutenant General Chun said.
"I think regardless of North Korean or South Korean wishes to try to be neutral in that situation, I think yes, we would be drawn into such a conflict."
