See Photos from the Early Days of the Korean War

On June 25, 1950, the Korean People’s Army of North Korea, with the backing of Joseph Stalin and against the backdrop of rising Cold War tensions, invaded South Korea. Two days later, having condemned the attack, the United Nations Security Council passed a resolution recommending military assistance to the Republic of Korea, now known as South Korea. By July, the U.S. was embroiled in a war that would last three years and cost more than a million lives in battle and hundreds of thousands more among civilians.

Less than a month after fighting began, LIFE published a series of photos by photographer Carl Mydans, who had documented the U.S. Army’s 1st Cavalry Division’s landing in P’ohang-dong on July 18. Mydans captured the unease of entering the unknown—in a very literal sense, as members of the Division set sail from Japan without knowing their destination. Two weeks later, the Battle of P’ohang-dong would begin, lasting for 15 days and ending with a victory for the U.N. Forces.

As Mydans wrote to LIFE’s editors in the letter below, which accompanied his film, much of this war photography had to be reviewed and approved by the U.S. government before publication, as it might otherwise weaken the security of a nation at war.

Though the impact of the war is still extremely palpable in North and South Korea–where the demilitarized zone divides an economic power from an impoverished, disconnected country—the Korean War is often referred to as a forgotten war in U.S. history, sandwiched as it is between World War II and the Vietnam War. Many Americans even during wartime tuned out news from the front lines after realizing that the conflict wouldn’t likely escalate to the level of the recently concluded Second World War. Congress never issued a declaration of war, with President Harry S. Truman calling it a “police action.” It wasn’t until the late 1950s that Congress formally designated the conflict a war.

But photographs like Mydans’, and those made by his LIFE colleagues David Douglas Duncan, Margaret Bourke-White and Michael Rougier, ensure that the war can never truly be forgotten. Though Mydans’ early photos document the quiet days before battle, it’s impossible to look at them now without knowing the horrors that each of those men would face in short order.

Liz Ronk, who edited this gallery, is the Photo Editor for LIFE.com. Follow her on Twitter @lizabethronk.