His desire after completing high school was to attend the National Military Academy (Indonesian: Akademi Militer Nasional).

The compromise was for Pierre to attend the Army's Engineering Academy (Indonesian: Akademi Teknik Angkatan Darat (ATEKAD)) in Bandung, where he started in 1958.

[1] Tendean received battlefield experience while in the academy when he was sent to West Sumatra with his fellow cadets to participate in operation Sapta Marga against the Revolutionary Government of the Republic of Indonesia (PRRI).

At that time Tendean was a Corporal Cadet and was assigned to the Army's Corps of Engineers (Indonesian: Zeni Tempur).

On 15 April 1965, Tendean was promoted to First Lieutenant (Indonesian: Letnan Satu (Lettu) Czi) and later, was assigned as a personal aide to General Abdul Haris Nasution.

[3] In the early morning hours of October 1, 1965, troops loyal to the 30 September Movement (G30S) came to Nasution's house with the intention of kidnapping him.