At the age of 18, I was admitted to the Communist Party of Vietnam and immediately entrusted with the responsibility of serving as Secretary of the Nam Thuong Commune Youth Union (now Dong Son Commune, Nam Truc, Nam Dinh) while still a probationary Party member. In September 1966, I enlisted in Division 330. After three months of training, I was selected to attend a “special cadre” course thanks to my “three-generation clean” personal background at the Technical Training School of the General Staff (the Cryptography Technical School) based at Thanh Do, Phuc Yen Town, Vinh Phuc. I was assigned to Class 167C, the very first technical cryptography (KTC) class of the Cipher Department, which gathered over 50 officers from the Army, Police, and civil administration.

It was here that I was first introduced to “Tano,” “Code translation,” and cryptographic slang such as “I, Rong, Canh”—letters I, R, Q—strange yet fascinating. We all understood that in the Cipher Department, loyalty was paramount, bound to the motto “Secrecy, accuracy, timeliness,” and prepared ourselves to dive into the world of the “six Ms”: “Vast – Exhausting – Eye-straining,” testing our very minds against an endless sea of letters and numbers.

Unlike numerical techniques (five-digit groups), learning KTC (three-letter dictionaries, five-letter code groups) was extremely difficult—one mistake could derail the entire transmission. But thanks to aptitude and diligence, I graduated with honors and was selected for assignment to the Central Unification Committee, along with Lieutenant Nguyen Ngoc Trac and Sergeant Nguyen Van Su, to reinforce the Cipher Department of B3 Front (Central Highlands).

After three grueling months marching across the Truong Son mountains, burdened with 40 kilograms of gear and a K54 pistol, we bid farewell to the North with solemn vows: “Leaving the North with waves of farewell / Welcomed by the South with overflowing affection” and “We shall not return home until the enemy is defeated.” In the spirit of Ho Chi Minh’s generation, the entire nation rose to the battlefield.

By July 1968, we reached B3 Headquarters in northern Kon Tum, stationed at MoRay, H67, Sa Thay. We were received by Captain Do Bong from Hai Duong, Head of the Cipher Section (Ban 6), and nearly 30 staff members. From then, we shared five arduous years together—facing hunger, malaria, relentless B-52 and B-57 bombings, and witnessing the forests of the Central Highlands and the lives of ethnic Ba Na and Ede communities ravaged by chemical warfare. Many comrades perished; the survivors carried dioxin’s lifelong toll.

As the only ones trained in the new KTC techniques, the three of us were placed in Team 1—the strategic unit responsible for receiving direct orders from the Central Military Commission, the B2 Command (Central Office for South Vietnam), and Military Region 5, then transmitting them to Major General Hoang Minh Thao, Commander of B3. I was assigned to decode “immediate” top-secret cables—sometimes explicitly marked “to be decoded only by designated personnel”—sent from Hanoi, COSVN, and the Military Regions.

Over five years at B3, through intellect and determination, I decoded thousands of strategic and tactical messages for General Hoang Minh Thao. These became the bedrock for key campaigns, culminating in the historic breakthrough of Buon Ma Thuot on March 10, 1975—shattering the South’s strongest defense line, paving the way for the Ho Chi Minh Campaign and national reunification. Among the countless “urgent decode” cables, three pivotal moments remain etched in my memory:

1. The Last Days of President Ho Chi Minh (August 1969)

By early August, his health had deteriorated. The Central Military Commission sent updates every five days, then every two. On August 25, reports noted severe weakness; on August 28, arrhythmia; by August 30, worsening conditions. On September 1, the Politburo planned to honor his wish to attend National Day, but it was impossible. At 9 p.m. on September 2, 1969, I decoded a cable signed by General Vo Nguyen Giap: President Ho Chi Minh had passed away at 9:47 a.m. that day. General Hoang Minh Thao fainted upon receiving the news.

2. The Battle of Dak To – Tan Canh (1972)

In April 1972, alongside Quang Tri and Xuan Loc, the Central Highlands launched a campaign to liberate Dak To – Tan Canh within 24 hours, then move on Kon Tum. With overwhelming firepower—including T-54 tanks and B72 anti-tank missiles supplied via the Ho Chi Minh Trail—our forces captured Dak To – Tan Canh in just seven hours on April 24. I personally decoded General Vo Nguyen Giap’s congratulatory message praising the operation as a “perfect combined-arms battle.” Yet torrential rains and strained supply lines stalled progress at Kon Tum, leading to heavy casualties—about 500 per day. General Giap then cabled an urgent order: “At all costs, open a blood road to withdraw forces and preserve strength.”

3. The Paris Peace Accords (1968–1973)

After 201 public sessions and 45 private talks between Special Advisor Le Duc Tho and Henry Kissinger, the U.S. conceded defeat. At 12:30 p.m. on January 23, 1973, the draft accord was initialed; on January 27, it was signed by the foreign ministers of the four parties. At 6 a.m. on January 28, I decoded the Central Military Commission’s historic cable announcing the agreement. Joy erupted across the Central Highlands—soldiers embraced, shouting: “We’re going home soon!” Tears of relief filled the forest as hope of reunion with family drew near. Yet it would take two more years, until April 30, 1975, and immense sacrifice, before the dream of reunification became reality.

After the accords, I returned North and joined the newly formed 1st Corps (Army Corps 1 – the “Determined Victory” Corps). As part of its political cadre, I participated in its second march South in 1975. On April 30, units of the Corps captured the Saigon regime’s Ministry of Defense and General Staff Headquarters, coordinating with other corps to seal the historic victory of the Ho Chi Minh Campaign.

The Cipher Department is one of Vietnam’s most secretive sectors, its legacy written in silent sacrifices across wars against the French, Americans, and beyond. My generation endured immense hardship and loss, yet with loyalty and intellect, we ensured the Party’s and military’s commands reached the front lines. Today, with modern technology and youthful vigor, I believe future generations of cipher officers will achieve even greater successes—adding new chapters to the golden history of Vietnam’s Cipher Department.