The retired general died at the Roman Catholic Hospital in the early hours of Sunday morning after a short illness.
A close relative told Nampa that Hamaambo complained on Saturday afternoon to his driver that he was not feeling well when the two were travelling from the north of the country to Windhoek.
He was immediately taken to the Windhoek Central Hospital, after which he was transferred to the Roman Catholic Hospital the same day.
He was operated on Saturday evening at around 19:00 while at the Roman Catholic Hospital's ICU.
Hamaambo spent 23 years as the commander of the South West African People's Organisation's military wing.
He was the NDF's chief since its formation in 1990, shortly after Namibia obtained its independence.
Hamaambo officially retired in November 2000 when he handed over the reins to Lieutenant General Solomon Hawala.