In this new configuration, the Perch had accommodations for 115 troops, and the hangar could accommodate a landing vehicle tracked (LVT) capable of carrying a jeep and towed 75 mm cannon or eight 10-man rubber boats. In the months leading up to the Korean War, the Perch participated in numerous troop and cargo-carrying exercises.

On the morning of June 25, 1950, six divisions of the North Korean Army crossed the 38th parallel that divided the peninsula into North and South Korea. The Korean War had begun.

The Perch arrived in Japan in August and was soon joined by Royal Marines from Great Britain’s 41 (Independent) Commando under the command of World War II veteran Lt. Col. Douglas B. Drysdale. 41 Commando had been formed on Aug. 16 to assist in offensive operations against communist troops. The “Independent” designation gave Drysdale broader authority than normal, because it meant that he, and not his superiors in British headquarters, was responsible for all operational and logistical matters. The unit would later achieve notoriety in the Battle of Chosin Reservoir when, as part of Task Force Drysdale, it fought its way through Hell Fire Valley. 41 Commando later received the Presidential Unit Citation.

The unit arrived at Camp McGill, the U.S. Army post near the U.S. Navy base at Yokosuka, in late August. One of the first decisions regarding the unit was the issuance of quantities of American military gear and weapons for its use in order to simplify logistics issues. Intensive training ensued.

One individual who was skeptical of the British Commandos proposed contribution was the supreme commander of U.N. forces, General of the Army Douglas MacArthur. MacArthur, an Anglophobe, bluntly questioned the utility of the British Marines in raids to Vice Adm. C. Turner Joy, commander, Naval Forces, Far East. Joy did not share MacArthur’s prejudices and was a vocal proponent of special operations raids using the Commandos. In a rebuttal, Joy wrote, “The 41 Royal Marine Commando was formed and trained especially to conduct commando raids. Plans are ready for destruction of several key points between latitudes 40 and 41 on [the] east coast. Believe they can be executed without serious risk. Submarine crew and commandos are keen to fight and gain experience for evaluation of this type of organization.” Joy was able to carry the day against the general, which was no small achievement.

Within a month of its arrival, a detachment of 41 Commando assisted in the Inchon landing. The unit’s first large-scale mission occurred on North Korea’s east coast about two weeks later; a sabotage mission in support of the post-Inchon offensive campaign to destroy rail tunnels on North Korea’s east coast, north of Hungnam. Previously the tunnels and rail lines had been hit by air strikes, but damage was minimal. Obeying MacArthur’s strict orders that capped the size of a special operations mission force at 70 men, Drysdale organized for the raid a contingent composed of himself, three officers, and 63 non-commissioned officers and men.

The plan called for a raid on two railroad bed and railway tunnel targets. The Perch, supported by the destroyers USS Maddox (DD 731) and USS Herbert J. Thomas (DD 883), would carry the Commandos to a predetermined location off the North Korean coast. Transport to and from the beach would be by inflatable launch rafts towed by a motorized skimmer that were all contained in the Perch’s afterdeck hangar. Intelligence for the mission was a mixture of good and bad. Reconnaissance photos were clear and gave much valuable information, but maps and charts were poor. Little was known about the sea depths and beach conditions around the landing site. Underwater mines, enemy patrol boats, and land patrols were another concern. Still, the risks were judged acceptable, and, on Sept. 25, the Perch entered the Sea of Japan and set course for North Korea.

BBC journalist and Member of Parliament Thomas E. Driberg had a rare opportunity to accompany 41 Commando on some of its missions. In a report broadcast on Dec. 20, 1950, he said, “These lads grew remarkably quickly into the mood and outlook that seem to be characteristic of this special kind of outfit: One might define it as a nonchalant self-sufficiency, a debonair assurance that is never arrogant, a self-mocking toughness. The common idea of Commando ‘toughness’ is wrong. They are not muscle-bound supermen. Many of them are quite slight and trim – physically compact, mentally alert. Their training fits them perfectly for such jobs as they had to do.”

The log of the Perch confirmed the high morale and ability of its passengers as well as how quickly the two disparate groups of sailors and Royal Marines melded into a team, particularly since they had only been together for two weeks. One entry in the Perch’s log noted, “The Royal Marines were experienced raiders with a ‘can do’ attitude comparable to that of the Perch’s. They seemed to enjoy having more thrown at them than they could possibly assimilate in the short time available, and rose to the occasion by becoming a well-trained and coordinated submarine raiding team in a remarkably short time.”