WASHBURN, Wis. (AP) – A Wisconsin Marine who died in Vietnam will be buried off Lake Superior this weekend, 46 years to the day he was killed in a helicopter crash.  Lance Cpl. Merlin R. Allen of Bayfield was 20 years old when his helicopter was trying to land in hostile territory in Vietnam. As the aircraft approached the landing zone it was hit by enemy fire, causing the helicopter to ignite and crash-land.   Allen was one of five people who were killed. His remains weren’t immediately recoverable, but a joint U.S. and Vietnamese team excavated the crash site last year and found the remains.  He’ll be buried Sunday in Washburn.