On the eve of the Korean War the United States armed forces conducted the largest Joint, airborne, and amphibious maneuvers ever staged in peacetime, the Puerto Rico Exercises (PORTREX). The purpose of the exercises were four-fold: to provide training for three Services in the planning and execution of Joint operations; to test existing Joint doctrine and gather information concerning Joint amphibious-airborne operations; to test the capabilities of new equipment and their suitability for Joint operations; and to provide training for the defense forces of the Caribbean Command.  A fifth training objective, the simulation of the tactical employment of the atomic bomb, was canceled late in the planning phase. The maneuver phase of PORTREX began on 25 February and lasted until 11 March 1950.  Some 80,000 soldiers, sailors, airmen, and Marines participated in the exercise, which was controlled by 1,800 Marine Corps officer-empires, most of whom had seen combat in the Pacific during World War II.  The area selected for the exercises was the small, narrow island of Vieques, located off the eastern shore of Puerto Rico. The island was less than twenty miles long and only two to three miles wide. The United States had acquired about two thirds of Vieques in the 1940s and the Navy had used it since 1947 as a target and bombing range for the guns and planes of the Caribbean Fleet. The island also served as a training area for the Marines, who had staged amphibious landings there during the Atlantic Fleet exercises of 1948 and 1949.
    The PORTREX scenario called for the Aggressor Forces, which had captured Vieques and enslaved the inhabitants, to defend the island.  The Liberating Forces from the United States would conduct a seven-day air campaign, followed by an airborne and amphibious assault to drive the aggressor back into the sea and reestablish order in this Western-oriented republic.  Brigadier General Edwin L. Sibert commanded the Aggressor ground forces, which were composed of troops from his Antilles Command. The 65th Infantry, the Regular Army's only Hispanic regiment, made up the core of the Aggressor ground forces. The regiment was a relatively well-led and well-trained post-World War II unit, having exercised with the Marines in amphibious operations on Vieques in both 1948 and 1949, first as a floating reserve and then as part of the amphibious assault force. For PORTREX the 65th was augmented with soldiers from 33rd Infantry Regiment, another largely Hispanic formation stationed in Panama. The Aggressor Forces were to be entrenched in defensive positions in the central part of Vieques, while the eastern tip of the island was to be used as an impact area for a live, pre-invasion naval and aerial bombardment.  The Liberating Forces consisted of a regimental and a battalion combat team from the 3d Infantry Division's 15th and 30th Infantry Regiments, along with a battalion combat team from the 82nd Airborne Division's 504th Parachute Infantry Regiment.  These 11,500 combat troops were augmented with another 4,100 support troops as well as large naval and air assets, including 17,000 Marines. Major General Percy W. Clarkson, the Commander of the 3d Infantry Division, commanded the Liberating Force ground forces.
Plans called for the Aggressor ground forces to fortify the impact area and build barricades, demolitions, and other obstacles on the beaches and defensive positions throughout the island. The men of the 65th and 33rd Infantry Regiments spent 70,000 man days digging defensive positions, constructing underground command posts (each large enough to house 15 to 20 indefinitely), creating vast and intricate obstacle zones, and installing 380 miles of barbed wire. They also registered their crew-served weapons, exercised their communications equipment, conducted refresher training, and rehearsed day and night counterattacks and withdrawals. “The Puerto Ricans of the defensive force who began by building installations that were really impregnable, went about behaving as though they were in the business of blood, sweat, and tears,” wrote Hanson W. Baldwin, the well-known and veteran New York Times war correspondent. “Their camouflage was excellent” and “their fields of fire were properly arranged.”
Early on the morning of 8 March, D-Day, the first Navy shells began exploding on Vieques, signaling the beginning of the ground battle.  The battleship U.S.S. Missouri fired 108 rounds from its massive sixteen-inch guns, while the remaining 150 ships of the Liberating Force fleet fired more than 20,000 eight-inch, six-inch, and five-inch rounds. Then Air Force bombers unleashed a long string of bombs. The explosions were felt throughout the island.  At about the same time, the 10,500 men of the 3d Infantry Division began to move toward Red and Blue Beaches on the island’s southern coast aboard hundreds of landing craft.  Yellow Beach, farther to the east, was slated to be used later to offload vehicles and other heavy equipment. Overhead Air Force and Navy fighters and fighter-bombers flew in support. On hand to observe the landings were Secretary of Defense Louis Johnson, Secretary of the Navy Francis P. Matthews, Chief of Naval operations Admiral Forrest P. Sherman, U.S. Senators and Representatives, and the senior uniformed officers of the four Services.  When the first wave of landing craft hit the beaches they were engulfed by concentrated mortar and artillery fires (simulated), which inflicted forty percent casualties and, along with the dense obstacles, stopped the landings cold. Umpires assessed that, instead of knocking holes in the Aggressor’s defense, the bombings had made them completely impassable.  The Liberating Forces suffered heavily as landing craft continued to bring in successive waves of personnel and equipment under the intense mortar and artillery barrage.  As engineers and bulldozers struggled unsuccessfully to open lanes through the tangled barbed wire, log barricades, and other obstacles, wheeled vehicles jammed up on the beaches, “and there is not much doubt,” wrote Baldwin, “that in actual war casualties would have been heavy.”  “Stopping the assault forces at the water’s edge proved that the Puerto Ricans could hold their own against the best-trained soldiers that the United States Army could put into the field,” wrote Colonel William W. Harris, the commander of the 65th Infantry Regiment.  In his short time as commander of the regiment, Harris had become the Army’s leading advocates of Hispanic troops. But PORTREX was far from over. The umpires called an administrative halt in the exercise and directed the Aggressor forces to clear eight to ten lanes through the beach obstacles so that the assaulting troops could come ashore.  In the meantime, waves of assault craft were diverted to the less heavily defended Yellow Beach. After the Aggressor forces had cleared the required number of lanes using tanks, the Liberating Forces continued their landings on Red and Blue Beaches. The men of the 3d Infantry Division lost no time in taking the fight back to the defenders and by the end of the day they had carved out a sizeable beachhead one to two thousand yards deep.
    The division spent its first night ashore reorganizing, consolidating their position, and preparing for an early morning assault.  At dawn the 3d Division attacked along a broad front.  Under heavy pressure, the defenders responded with a counterattack, preceded by heavy mortar and artillery fires.  At about the same time, the sound of low-flying C-119 Flying Boxcars alerted the Aggressor Forces that an airborne assault was imminent.  When the paratroopers of the 504th BCT hit the ground, the 65th Infantry hit them hard with preplanned artillery and mortar fires as well as with an attack by the reserve battalion. A bitter battle ensued and Major General P. J. Mueller, the Chief Ground Umpire, assessed that the airborne battalion had suffered fifty percent casualties as a result of the 65th Infantry’s attacks and that six of the C-82s had been shot down with a loss of 180 paratroopers. Another 100 paratroopers were assessed as killed in the air. Thus, almost a third of the almost 1,000 men that had jumped were assessed as killed even before they had reached the ground. The paratroopers incurred another ten percent casualties as the result of obstacles on the drop zone.  Finally, the men of the 504th BCT suffered sixty-one actual casualties (sprains, bruises, twisted backs, and some broken bones) when the men jumped in a fairly stiff breeze and landed in a mesquite-strewn area.  Still, the elite paratroopers managed to inflict thirty percent casualties on the 65th Infantry’s reserve battalion in the fighting.  And later that evening they drove the Puerto Ricans off the critical high ground overlooking the beachhead.  The stage was now set for an early morning breakout by the men of the 3d Infantry Division. But by the following morning the attack had ground to a halt. Colonel Harris later discovered that Lieutenant General John R. Hodges, commanding all the invasion forces, Rear Admiral Harold D. U. Baker, commanding the amphibious attack forces, and Major General Clarkson, commanding the ground forces, had been declared casualties. They had been met by a Puerto Rican soldier dressed in native working clothes, who had handed the assembled commanders a small present as a token of appreciation for their liberation. “When the General opened the package in the presence of the admiral and a pre-briefed umpire,” recalled Harris, “a small puff of smoke came out of the box. Inside was a note which said, ‘This is a booby trap – you are now dead.’”  “General Hodges and Clarkson and Admiral Baker were ‘restored to life’ by the umpires within an hour or so,” reported Baldwin.  “In the meantime their staffs and subordinates carried the burden of command, and all hands learned a realistic lesson in security.”
    Colonel Harris, now commanding all Aggressor Forces on the island, decided to take advantage of the resulting loss of momentum in the 3d Infantry Division attack.  That evening the regiment launched a spoiling attack with infantry, tanks, and half-track mounted four-barrel .50 caliber machineguns, preceded by an intense artillery barrage along with smoke. The tanks quickly punched through the defenses of the Liberating Forces, followed by the infantry, shot up the 3d Infantry Division command post, and fought their way to the beaches shortly after breaking through. The Aggressor Forces, however, were met with forty-two on-call aircraft, each armed with three 500 pound bombs, which struck the tanks and inflicted seventy-five percent casualties on the attacking force, but only after considerable confusion and loss had been caused among the Liberating Forces, delaying a planned attack.
The 3d Infantry Division did not regain renew it assault until late in the afternoon of the third day. That attack soon forced the 65th Infantry to withdraw northward to a second prepared defensive position, but not before the artillery and mortars of the Aggressor Forces had inflicted more than 300 casualties on the attackers. The next morning the men of the 3d Infantry Division shifted their main effort and even a battalion counterattack by the Aggressor Forces could not slow their onslaught, forcing the Puerto Ricans to pull back once again. “By a series of counterattacks, shifting of artillery and mortar fires and some good footwork we were able to avoid disaster and stay alive,” remembered Harris. But the situation appeared grim for the Aggressor Forces. By the morning of D+5 the Liberating Forces had driven the 65th to the far side of the island and their last prepared defensive positions. Behind them lay Purple Beach and the waters of Vieques Sound. The men of the 65th and 33rd Infantry had almost reached the limits of their endurance.  Two days still remained in the exercise and the 3d Infantry Division was building up for one final all out assault to be delivered the following morning. In response, Harris planned to launch a battalion-size preemptive attack with infantry, tanks, and artillery, in order to win some time and stave off final defeat for as long as possible. The morning of D+6 opened with a roar as the Navy and Air Force began their pre-attack bombardments.  The 3d Infantry Division’s final attack was just starting when the order was given for the 65th Infantry counterattack to begin. Before it could be launched, however, an umpire informed Colonel Harris that PORTREX had ended and that the regiment would receive credit for the attack.
By the end of PORTREX Liberating Forces had overrun two-third of Vieques and put ashore 14,250 men, 1,600 vehicles, and 35,000 tons of cargo.  Another almost 1,000 men and additional supplies had also been dropped from the air.  Baldwin reported that PORTREX “shattered a number of precedents” and “opened a new chapter in the technique of amphibious and joint operations….The training was hard and realistic and the whole maneuver better conducted  and the troops, particularly the defense troops, in a higher state of training than in any other amphibious maneuver conducted since the war.”  While the fundamental purpose of the exercise had been to provide training in Joint planning and operations, a number of other valuable training benefits had also resulted. The Army and the 3d Infantry Division received training in large-scale troop movements and amphibious landings. In addition, the 65th Infantry and one battalion of the 33rd Infantry received training in defensive tactics which, to some qualified observers, were superior to those of the Japanese in World War II. The 504th BCT had trained in overseas airborne operations along with its airlift unit, the 314th Troop Carrier Group. And the three top command echelons received valuable experience in Joint planning and cooperation. That experience would pay major dividends less than six months later.
    On 15 September 1950 the 1st  Marine Division and 7th Infantry Division of the U.S. Army’s X Corps, supported by the might of the U.S. Navy and Air Force, conducted the largest amphibious assault since World War II at Inchon, on Korea’s western coast. Operation CHROMITE, the Inchon landing, was one of the U.S. military’s boldest and most successful joint assaults ever. By the time it was over, Seoul had been liberated, the North Korean People’s Army shattered, with some 14,000 killed and another 7,000 captured, and the United States military had regained the initiative and was on the attack.  Later that same month, the 65th Infantry Regiment arrived in Korea along with the 3rd Battalion, 33rd Infantry Regiment, which would serve as the regiment’s third infantry battalion for the duration of the war. The successful combination during PORTREX had prompted the Army’s leadership to deploy both units to Korea. In November, after briefly serving with the 2nd and 25th Infantry Divisions, the 65th Infantry joined the 3d Infantry Division in North Korea as that unit’s third infantry regiment (the 30th Infantry having been stripped of personnel to fill the 7th and 15 Infantry Regiments and left behind in the United States). The Liberators and Aggressors of PORTREX would fight side-by-side for the next four years to ensure a free and independent South Korea.

Colonel Gilberto Villahermosa is the Chief, Combined Joint Task Force Coordination Branch at NATO’s Regional Headquarters Allied Forces North, Brunssum, The Netherlands. His articles have appeared in a number of magazines, including Armor, Army, Military History, and Napoleon.
Maps and Photos
Color Map of Puerto Rico.
Color Map of Vieques (United States Navy)
Puerto Rican soldiers of the 65th Infantry Regiment transferring to a landing craft during amphibious training.  In 1949 the 65th Infantry served as an amphibious reserve during the Atlantic Fleet maneuvers. (Captain Thomas Guffain)
Colonel William W. Harris, who commanded the 65th Infantry Regiment during PORTREX, became one of the Army’s leading advocates of Hispanic troops. Six months after the exercise Harris and his regiment found themselves in Korea. (National Archives)

Using scaling ladders, men of the United States Marines storm ashore at Inchon on 15 September 1950. PORTREX laid the foundation for Joint cooperation and success at Inchon. (National Archives)
Sources

Hanson W. Baldwin, “Vieques ‘Invasion’ Slated for Today,” The New York Times,
March 8, 1950, p. 13.

Hanson W. Baldwin, “D-Day on Vieques Finds Going Tough,” The New York Times,
March 9, 1950, p. 3.

Hanson W. Baldwin, “Navy Withdrawing in Caribbean Area,” The New York Times,
March 10, 1950, p. 4.

Hanson W. Baldwin, “Last Action Today in Caribbean War,” The New York Times,
March 11, 1950, p. 6.

Hanson W. Baldwin, “Vieques ‘Captured’ As Exercise Ends,” The New York Times,
March 12, 1950, p. 33.

Hanson W. Baldwin, “Portrex May Bring Operating Changes,” The New York Times,
March 14, 1950, p. 2.

Critique Joint Puerto Rican Exercise, FY 1950 Held at Vieques Island, Puerto Rico,
12 March 1950. Record Group 338 Records of the U.S. Army Commands, 1942,
U.S. Army Caribbean  1947-64, Box 44 Defense Plans and Maneuver Reports
1947-50, National Archives and Records Administration, Washington D.C.

Directive for Implementing the Army’s Participation in Joint Puerto Rican
Exercises, Fiscal Year 1950, Department of the Army, Office of the Adjutant
General, Washington D.C., 7 November 1949, p. 2. “3rd Infantry Division,”
U.S. Army Center of Military History, Force Structure and Unit History Branch.

Colonel (Retired) William W. Harris, Puerto Rico’s Fighting 65th U.S. Infantry
(Novato, California: Presidio Press, 1980).

Jean R. Moenk, A History of Large-Scale Army Maneuvers in the United States,
1935-1964 (Historical Branch, Office of the Deputy Chief of Staff for Military
Operations and Reserve Force, U.S. Continental Army Command: Fort Monroe,
 Virginia, December 1969).

Colonel (Retired) Harry G. Summers, Jr., “Inchon Invasion (Operation Chromite),”
Korean War Almanac (New York: Facts on File, 1990)

Report on Participation on Exercise PORTREX, Headquarters, Army Forces,
Exercise PORTREX, Ft. Benning, Georgia, 15 April 1950, p. 5,
Record Group 338, Box 44 Defense Plans and Maneuver Reports 1947-50, NARA.