"On 19 August 1966, SEAL Team One suffered its first combat fatality in Vietnam. While on a recon mission, a patrol had discovered a series of bunkers and weapons positions along the Dinh Ba River, thirteen miles south-east of Nha Be. They were extracted and reinserted further up river to pinpoint two reported camouflaged sampans that had been spotted by a helicopter. Fresh tracks were discovered, and the sampans were then sighted about five hundred meters from the SEAL's position. Petty Officer Billy W. Machen was acting as point man. Coming to a clearing in the jungle growth, he halted the unit and moved ahead into the opening to reconnoiter. As he paused and searched the surrounding area, he suddenly realized the VC were lying in ambush and he was in the middle of the kill zone. Rather than make a futile attempt to seek cover or retrace his steps and thereby pinpoint the patrol's exact location, Machen initiated fire and attacked the enemy unit, forcing them to trigger their ambush prematurely. Immediately after, automatic weapons fire from both banks of the river erupted. The SEAL patrol was alerted to the danger and was able to gain cover, return fire, and engage to suppress the VC attack. Machen was killed in the initial fusillade. He was posthumously awarded the Silver Star, the nation's third highest medal for valor."
Information obtained from T. L. Bosiljevac's Book "SEALs UDT/SEAL Operations in Vietnam"