For conspicuous gallantry and intrepidity at the risk of his life above and beyond the call of duty as pilot and aircraft commander of a search and rescue helicopter, attached to Helicopter Support Squadron 7, during operations against enemy forces in North Vietnam. Launched shortly after midnight to attempt the rescue of 2 downed aviators, Lt. (then Lt. (J.G.)) Lassen skillfully piloted his aircraft over unknown and hostile terrain to a steep, tree-covered hill on which the survivors had been located. Although enemy fire was being directed at the helicopter, he initially landed in a clear area near the base of the hill, but, due to the dense undergrowth, the survivors could not reach the helicopter. With the aid of flare illumination, Lt. Lassen successfully accomplished a hover between 2 trees at the survivors' position Illumination was abruptly lost as the last of the flares were expended, and the helicopter collided with a tree, commencing a sharp descent. Expertly righting his aircraft and maneuvering clear, Lt. Lassen remained in the area, determined to make another rescue attempt, and encouraged the downed aviators while awaiting resumption of flare illumination. After another unsuccessful, illuminated rescue attempt, and with his fuel dangerously low and his aircraft significantly damaged, he launched again and commenced another approach in the face of the continuing enemy opposition. When flare illumination was again lost, Lt. Lassen, fully aware of the dangers in clearly revealing his position to the enemy, turned on his landing lights and completed the landing. On this attempt, the survivors were able to make their way to the helicopter. En route to the coast he encountered and successfully evaded additional hostile antiaircraft fire and, with fuel for only 5 minutes of flight remaining, landed safely aboard U.S.S. Jouett (DLG-29).