South Korea needs 500,000 active troops to counter potential NK attacks: study

North Korean leader Kim Jong-un watches an artillery firing drill by combined artillery units of the Korean People’s Army, Wednesday, in this image carried by the North's official Korean Central Television, Thursday. Yonhap

South Korea must maintain at least 500,000 active-duty troops to defend against potential surprise attacks from North Korea, according to a new military study released Sunday. The report highlights growing concerns over the nation's shrinking pool of conscripts due to its declining birthrate.

Published in the summer edition of Defense Policy Studies, the study determined the minimum troop requirement by applying the U.S. Army’s minimum planning ratio doctrine to the Korean Peninsula. Under this doctrine, a defending force should be able to hold their position against an attacker with a troop ratio of 1 to 3, whereas an attacker generally requires a ratio of 3 to 1.

The study, led by Kim Jeong-hyuck of the Korea Army Research Center for Future and Jee Hyo-keun of Konyang University, reported that as of 2022, North Korea had approximately 1.28 million troops, compared to South Korea’s 500,000 — representing a roughly 2.6 to 1 ratio. In the Army alone, the margin widened to almost 3 to 1, leaving Seoul’s forces “at the bare minimum for defense,” according to the authors.

South Korea’s wartime plans assume the quick mobilization of hundreds of thousands of reservists and timely U.S. support, but there is no certainty that these assumptions would hold in an actual crisis,” the authors wrote. They added that, given the current numbers, the chances of success in the opening stages of a North Korean assault are limited.

The researchers also warned that technological superiority alone would not eliminate the disparity.

“Maintaining a standing force of 500,000 troops is of critical importance to South Korea, as it relies on a defend-then-counterattack strategy,” the paper noted.

Lessons from the Russia-Ukraine conflict were also cited. Although Russia entered the war with an overall manpower advantage of 4 to 1, the ground troops deployed initially were closer to a ratio of 1 to 1.3, leaving Moscow struggling in the first phase of fighting, the study pointed out.

The report highlights South Korea’s deepening conscription crisis. If the current birthrate trend continues, the number of 20-year-old men could fall to around 140,000 by 2040, making it difficult to keep even 300,000 soldiers in uniform. The study therefore calls for “national-level decisions,” such as revising the length of military service, combining the draft with voluntary enlistment and hiring more civilians for noncombat roles.

However, the Ministry of National Defense has vowed to maintain the troop level at 500,000 under its 2025-29 medium-term defense plan. This involves converting some enlisted troops into noncommissioned officers, expanding the civilian workforce in logistics, administration and training and allocating personnel to new areas such as artificial intelligence, space and electromagnetic warfare.

“The findings emphasize the growing pressure on South Korea to maintain a sufficient number of troops to deter North Korea while coping with a shrinking and aging population — a dilemma that could influence defense planning for years to come,” Kim said in the report.