Text dexcribing my military service - not sure if correct, grammar-wise.
Hey, I could use some help :)

I had been recruited to the Military on the 20th of October, 2013. As a combat service supporter in the Teleprocessing Corps, I had been through two months of boot camp, and after I'd finished the training, I was stationed in the Ranger's unit teleprocessing battalion, serving in the southern city of ****. I've had participated in the 2014 operation *** *****, and after that, I joined the commander's course. And that's how I finished my military service after three years.

This is the order:
1. Joined the military.
2. Boot camp for two months.
3. finished the training
4. Stationed in Rangers and as serving there for a while.
5. Participated in an operation.
6. Joined commanding course
7. Finished my service.

No longer a soldier.

Is the grammar on this ext correct? The usage of had been and the other perfect tenses?

Question

Text dexcribing my military service - not sure if correct, grammar-wise.
Hey, I could use some help :)

I had been recruited to the Military on the 20th of October, 2013. As a combat service supporter in the Teleprocessing Corps, I had been through two months of boot camp, and after I'd finished the training, I was stationed in the Ranger's unit teleprocessing battalion, serving in the southern city of ****. I've had participated in the 2014 operation *** *****, and after that, I joined the commander's course. And that's how I finished my military service after three years.

This is the order:
1. Joined the military.
2. Boot camp for two months.
3. finished the training
4. Stationed in Rangers and as serving there for a while.
5. Participated in an operation.
6. Joined commanding course
7. Finished my service.

No longer a soldier.

Is the grammar on this ext correct? The usage of had been and the other perfect tenses?

Answer

Karen is correct.

Your story should use the simple past.

The past perfect is used to show that one event in the past occurred before another event in the past.

Here are some simple examples.

#1 [all verbs in the simple past because the time order is clear]
Yesterday at 9 a.m., I went to work.
At 10 a.m., the mail carrier delivered a box.
At 11:30 a.m., I came home.  I saw the box.

#2 [one verb in the past perfect to show the time order]
Yesterday at 9 a.m., I went to work.
At 11:30 a.m., I came home.  
I saw a box that the mail carrier had delivered.

More information about the past perfect here:
https://www.ef.com/ca/english-resources/english-grammar/past-perfect-tense/

Answer

You can use the simple past.  To use the perfect is incorrect in this case. I was recruited.... went through..... I finished... I was stationed... I participated.... I joined.... I finished.