The foreign affairs department has defended consultations efforts with Vietnam after a last-minute decision by Hanoi to ban 50th anniversary commemorations for the Battle of Long Tan.
At the time Veterans Affairs Minister Dan Tehan described the announcement as a "kick in the guts".
An estimated 1200 veterans travelled to Vietnam and while some small groups were allowed access to the site many veterans missed out.
New DFAT secretary Frances Adamson told a Senate estimates hearing in Canberra on Thursday there had been 18 months of consultation between the Vietnamese government, posts in Hanoi and Ho Chi Minh city and Canberra.
Ms Adamson blamed heightened Australian media attention and the large numbers of veterans travelling to Vietnam for spooking the country's government.
Officials denied they had any knowledge there was a risk the Hanoi would pull the plug on the commemorations before they were notified on August 16.
