| 25 June |
North Korea (NK) invades the Republic of Korea (ROK) with the backing of the USSR. |
| 27 June |
US forces authorized to conduct air and naval operations in support of the ROK south of the 38th Parallel. UN passes resolution authorizing armed force to restore peace. US Reserve forces authorized for call-up. |
| 28 June |
Seoul seized by NK. US Seventh Fleet assigned to Naval Forces, Far East. |
| 29 June |
Naval blockade of Korea authorized and first US Navy offensive actions occur. Offensive air operations authorized in NK. US ground forces authorized for commitment to ROK in support role. |
| 30 June |
US ground forces authorized for commitment to ROK for combat operations. |
| 1 July |
US Task Force Smith, deployed by 24th US InfDiv, arrives. |
| 3 July |
First UN carrier air strikes executed in NK. Inch’on seized by NK. |
| 5 July |
Task Force Smith defeated by NK forces in first US ground action. |
| 7 July |
1st Prov MarBde formed for immediate duty in ROK. |
| 12–14 July |
1st Prov MarBde departs for ROK. |
| 13 July |
Eighth US Army in Korea headquarters formed. |
| 14 July |
ROK forces placed under United Nations command. |
| 17 July |
ROK forces delegated to Eighth US Army. |
| 2 August |
1st Prov MarBde arrives at Pusan. |
| 4 August |
Pusan (aka Naktong) perimeter established as UN forces are pushed into the southeast corner of Korea. |
| 8–18 August |
Battle of Naktong defeats NK penetration of Pusan perimeter. |
| 10–22 August |
1st MarDiv (-) departs for Japan. |
| 15 August |
Korean Augmentation to the US Army approved. |
| 23 August |
Decision made to land at Inch’on. |
| 26 August |
X US Corps activated in Japan. |
| 28 August |
X US Corps issues Operation Order 1 for Inch’on. |
| 30 August |
Naval Forces Far East issues Operation Plan 108-50 assigning JTF7 the mission of seizing Inch’on. |
| 31 Aug–19 Sep |
Second battle of the Naktong. |
| 1 September |
Reconnaissance of Inch’on Harbor and approaches commence. |
| 3 September |
Korean Marine Regiment attached to 1st MarDiv. |
| 4 September |
1st MarDiv issues Operation Order 2-50 for Inch’on. JTF7 and TF90 orders are issued concurrently. |
| 5–12 September |
1st MarDiv departs Japan for Inch’on. |
| 13 September |
1st Prov MarBde departs Pusan for Inch’on. |
| 10 September |
Preliminary air attacks commence in Inch’on area. |
| 11 September |
JTF7 formally activated to execute landing. |
| 13 September |
1st Prov MarBde re-absorbed into 1st MarDiv and departs Pusan for Inch’on. Pre-landing bombardment commences. |
| 15 September |
1st MarDiv lands at Inch’on. |
| 16 September |
Inch’on secured. |
| 16–22 September |
Eighth US Army breaks out of Pusan perimeter. |
| 17 September |
NK counterattacks outside of Inch’on. Ascom City and Kimpo Airfield secured. 7th InfDiv arrives at Pusan. 7th Marines departs Japan for Inch’on. |
| 18 September |
7th InfDiv begins debarking at Inch’on. |
| 20 September |
5th Marines cross Han River. NK counterattacks outside Yongdungp’o. |
| 21 September |
Yongdungp’o secured. 7th Marines arrive at Inch’on. |
| 22–24 September |
Approaches to Seoul secured and NK main defenses penetrated. |
| 24 September |
1st Marines cross Han River into southwest Seoul. |
| 25 September |
1st MarDiv launches main attack into west Seoul. RCT-32 crosses Han River into south Seoul. |
| 26 September |
Eighth Army elements from Pusan and X Corps troops from Inch’on link up at Osan. |
| 27 September |
Seoul liberated by US and ROK forces. |
| 28 Sep–3 Oct |
UN forces continue to drive north from Seoul and secures Uijongbu. |
| 29 September |
Seoul re-established as capital of ROK. |
| 30 September |
ROK forces cross the 38th Parallel. |
| 4 October |
China decides to intervene in Korea. |
| 5 October |
Inch’on–Seoul Campaign completed. |
| 6–8 October |
X Corps assembles at Inch’on and begins embarkation for Wonsan. |
| 9 October |
First US forces cross the 38th Parallel. |
| 25 October |
China commences surprise offensive into NK. |
