Cartagena reenlisted in the Army in 1947 and was serving in Company H, 65th Infantry Regiment when he participated in Operation "PORTREX"
65th Infantry Regiment (United States) which took place in Vieques. Upon the outbreak of the Korean War, Cartagena was assigned to Company C, 65th Infantry Regiment, 3rd Infantry Division and sent to Korea. The men of the 65th, now attached to the army's 3d Infantry Division, were among the first infantrymen to meet the enemy on the battlefields of Korea. After November, 1950, they fought daily against units of the Chinese
People's Liberation Army after the Chinese entered the war on the North Korean side. One of the hardships suffered by the Puerto Ricans was the lack of warm clothing during the cold and harsh winters. Among the battles and operations in which the 65th participated was
Operation Killer in January 1951, becoming the first regiment to cross the
Han River in South Korea during the operation. In April 1951, the Regiment participated in the Uijonbu Corridor drives. He earned the nickname "One Man Army". On April 19, 1951, Cartagena, "with no regard for his own safety," as the official record states, left his position and charged directly into devastating enemy fire, single-handedly destroying two enemy emplacements on Hill 206 near "Yonch'on,"
North Korea. After taking out the emplacements, he was knocked to the ground twice by exploding enemy grenades. Nevertheless, he got up and attacked three more times, each time destroying an enemy emplacement until he was wounded. On October 19, 2002, during a ceremony honoring the 65th Infantry, when he was asked about the battle, Cartagena responded that he just hurled back at the
Chinese the grenades thrown at him. He thought that the rest of the squad was behind him, and didn't realize most of them had been wounded and forced to take cover. Later they found 33 dead Chinese in the machine gun and automatic emplacements and they found 15 more dead in the positions he had destroyed on his way up the hill. where he was hospitalized for 62 days. According to 1st Lt. Reinaldo Deliz Santiago: Cartagena initially was awarded a
Silver Star which was later upgraded to the
Distinguished Service Cross, the second-highest military decoration of the United States Army (second to the Medal of Honor), awarded for extreme gallantry and risk of life in actual combat with an armed enemy force. ==Distinguished Service Cross citation==