The last U.S. soldier to leave Vietnam is believed to have died in the attack on the Pentagon.

Retired Master Sergeant Max Beilke was missing, presumed to be among those lying dead in the rubble of the defence headquarters, where he worked improving life for veterans.

Sgt. Beilke was listed by the U.S. Army as the last combat soldier to leave Saigon. The fall of Saigon to the North Vietnamese Army and the evacuation of the U.S. embassy occurred in 1975, but the official troop withdrawal, and Sgt. Beilke's historic place in it, was on March 29, 1973.

Many years later Sgt. Beilke, 69, was working on behalf of many of those with whom he had served, tackling veterans issues at the Pentagon. Every day he called his wife, Lisa, at 10 a.m. sharp. On Tuesday he did not call.

A general visited her on Wednesday and told her he had been to hospitals but could not find her husband.