Professor Nguyen Dinh Ngoc's path to intelligence work began when he witnessed his father's murder. His father's dying words were: "Stay, study hard, and help others. Our people suffer primarily from ignorance."

This ignited two passions within the young man: a love for mathematics and a burning desire for revenge against the invaders.

Professor, Doctor of Science Nguyen Dinh Ngoc. Photo: Vietnam Scientists Heritage Center.

A turning point came in 1953 when, at 21, Ngoc was fleeing conscription. He journeyed for three days and nights with a fellow escapee, who, upon reaching Vinh (Nghe An), revealed himself to be a revolutionary.

Ngoc was then introduced to Nguyen Huu Khieu, director of Inter-zone 4 Public Security, and began a year of training in telegraphy. He became a lone wolf agent, his identity known only to his direct commander.

Before his deployment, Khieu gave Ngoc half the stainless-steel band from an Omega watch, saying, "One day, someone will find you with the other half. If it fits, that's KD1, your direct contact."

The Party anticipated the Saigon government's attempts to sabotage reunification and elections. Long-term undercover agents were needed. Ngoc's mission: prioritize education and acquire credentials.

In 1954, Ngoc migrated south alone. In Saigon, he completed his bachelor's degree. Then came new instructions: "Seek further education abroad."

In November 1955, Ngoc went to France. Over the next 10 years, he earned five degrees in hydrometeorology, telecommunications, shipbuilding, and mathematics. Fluent in four languages, he lectured at French universities and worked at the Institut des Hautes Etudes Scientifiques (IHES).

An "eccentric professor" emerged. He was solitary, immersed in books, lecturing with one hand in his pocket, the other holding chalk, needing no notes, everything memorized.

This eccentricity served a purpose: memory training. Recalling classified plans or conversations verbatim was crucial.

In 1966, Ngoc returned to Vietnam. His lone wolf mission began in earnest.

At Saigon University of Science, his eccentricities intensified. He ate one meal daily, walked or cycled, lived austerely, and secured his door with seven locks. He walked backward (to expose followers), slept sitting up, or on newspaper-covered floors (practicing for capture).

His quirks intrigued even children. Once, a child asked why his hands were inside-out in his pockets. He quipped that his torn pants were inside-out, requiring reversed pockets.

Intelligence agent, Major General, Mathematics Professor Nguyen Dinh Ngoc. Photo: QDND

One Sunday, a student visited Ngoc. As others left, one lingered, asking, "Do you still have half an Omega watch band?"

Ngoc was stunned. The signal from over a decade ago. The student, KD1's liaison, instructed him to meet "Miss Phuong Lan" at Hue University.

There, Ngoc received the codename "Diep Son." His mission: infiltrate Saigon's intellectual and elite circles, including South Vietnamese generals and American advisors.

Besides his academic reputation, Ngoc offered fortune-telling, a mathematical trick that gained him trust and access to influential figures.

Learning of the US-South Vietnamese plan for Operation Cedar Falls, Diep Son wrote the information in invisible ink on a milk carton label, resealed it, and sent it to "Miss Phuong Lan." He then reported on Operation Junction City (November 1966), predicting increased US troop deployments in 1968.

Diep Son joined the Central Office for South Vietnam, working with Hai Tan, aka Nguyen Phuoc Tan (later Deputy Director General of General Department of Security).

Lieutenant General Nguyen Phuoc Tan recounted three of Ngoc's most significant achievements: providing 72-hour advance warning of a major US sweep in 1970, allowing the Central Office for South Vietnam to evacuate; forewarning of the Lon Nol-Sirik Matak coup against Sihanouk and the new pro-US government's threat to the National Liberation Front's Cambodian headquarters; and giving 24-hour notice that the US wouldn't aid Saigon during the 1975 Spring Offensive.

"I commanded many, but I trusted Nguyen Dinh Ngoc most. He exemplified courage and loyalty," said Lieutenant General Phuoc Tan.

Post-war, Ngoc joined the police, becoming Deputy Director then Director of Department V17 (Telecommunications and Informatics), retiring as a major general. He continued teaching and co-founded universities, leaving his mark on intelligence, science, and education.

Professor Ngoc helps his wife, Associate Professor, Dr. Truong My Dung, cross the street during a conference at Hanoi University of Science and Technology in 2005. Photo: Family provided

Intelligence work demands secrecy and sometimes endures misunderstanding. Ngoc remained discreet until his death in 2006, when Diep Son's story emerged.

His wife, Associate Professor Truong My Dung, remembered him as humble, rarely discussing himself, except once mentioning being investigated by the enemy, who left empty-handed. "Everyone saw his eccentricity, but few knew his courage and cunning, surviving amidst the enemy," she said.

She also recounted his handwritten copies of math books in French, German, and Russian, 60 of which she donated to the Vietnam Scientists Heritage Museum.

Professor Nguyen Huu Viet Hung considered Ngoc both teacher and friend. Major General Nguyen Dinh Ngoc reviewed both of Professor Hung's doctoral dissertations.

In 2007, after a Paris conference, a scholar of Jewish origin asked Hung, "Do you know Nguyen Dinh Ngoc?" They reminisced about their mutual friend, who had passed away a year earlier.

"Vietnamese diaspora is common. But few are remembered by international friends after 40-50 years," Professor Hung reflected. "Nguyen Dinh Ngoc's life is a novel."

Phan Duong

* Reference material: Novel "Don tuyen" - Pham Quang Dau.

* Documentary film "Intelligence Professor Nguyen Dinh Ngoc", directed by Nguyen Hai Anh.