other personnel were injured in the blast. FLEX 4 The Fleet Landing Exercise Number 4 was held from January 13 to March 15 in 1938. The Fleet Marine Force returned to the Caribbean to avoid any Japanese observation. The tests were conducted on the beaches of Vieques and the main island of Puerto Rico. During these exercises, three Army National Guard regiments participated by "defending" ashore while the Marines of the 1st Brigade attempted a "mock" assault against them. It was the first time that reconnaissance elements were added to the amphibious assault, reflecting the reconnaissance doctrine outlined in the Fleet Training Publication 167. The Army's contribution climbed to three infantry regiments with supporting arms and brigade alternated in the part of landing force and shoreline defender. Brigadier General James Roosevelt, eldest son of the late President Franklin D. Roosevelt, who as a lieutenant colonel was in the Marine Corps Reserve on active duty aboard the during one of the reconnaissance patrols and experiments with raiding and patrolling parties. These raiding and patrolling parties would lay the ground work for the Marine Raider Bn. 1st Marine Brigade tested the concept of delivering 4-man patrols by submarines. The exercise missions were a mixed success at Vieques and Puerto Rico when two patrols were captured, but it was realized that with experience and refinement the concept held promise. The Vieques Phase, three patrols of one Army and two Marines with four men each were assigned by Rear Admiral A. W. Johnson, Commander of the Attack Force, in reaching the beach under the cover of darkness by inflatable rafts. They launched from submarines , and with intentions of conducting a reconnaissance ashore and return to the submarines the following night at certain appointed rendezvous. Four Marines from the Headquarters Company of the 1st Brigade marked the first amphibious reconnaissance patrol launching from a submarine by raft in United States history. Those four Marines reported aboard S-47 but was unsuccessful in locating the beach on Vieques. "The weather conditions under which the night phase was carried on could not have been more adverse to a successful ship to shore movement. The heavy seas were awash the decks with every wave driven by a wind of between a force of 4 and 5 in velocity and varying direction from 70 degrees to 120 degrees which approximately paralleled the island. A brilliant full moon extended the