His subordinate was punished by the Army chief. Given sentence is in simple past tense and it is in active voice, we need to change it into passive voice. Rule : Subject + (was / were) + V3 + Optional Agents.
From Voice · English Language Competence Test
The doctor advised me to give up sweets.
Alexander expected to conquer the world.
Have you shut the window?
Don't laugh at me.
Why do you waste time?
People claim to have seen the suspect in several cities.
Where did you send the parcel?
He teaches us grammar.