In Jain Dharma, ahimsa is the highest principle, so joining the army is a serious ethical matter.

Can a Jain join the army?

From a Jain perspective, it is generally not ideal, because army service involves:

• training for violence,
• possible killing or harming living beings,
• support of weapons and warfare.

This directly conflicts with the spirit of ahimsa.

How does it affect the vow of ahimsa?

• For a lay Jain (shravak/shravika), the vow of ahimsa is already observed in a limited form, but one should still avoid intentional violence as much as possible.
• For a monk or nun, joining an army would be completely contrary to vows.
• For a layperson, active military service can create strong pap karmas, especially if it involves harming, killing, or approving violence.

In Jain ethics, even if one says, “I am only following orders,” the karmic responsibility does not disappear if violence is intentional or accepted.

How do we balance national duty and Jainism?

Jainism teaches that true duty should not violate dharma. So balance means:

• Serve the country in non-violent ways whenever possible.
• Protect society through education, medicine, administration, relief work, civil service, communication, rescue, or humanitarian work.
• Support the nation through truth, discipline, sacrifice, and self-control, without taking part in हिंसा.

A Jain should prefer:

• defense of life without aggression,
• non-violent service,
• peace-building,
• and practical ahimsa.

Simple Jain view

If a duty requires direct participation in killing, then it is difficult to reconcile with Jain ahimsa. If a duty serves the nation without violence, it is much more aligned with Jain values.

In short

• Army service is not compatible with the ideal Jain path.
• It may be seen as a grave compromise of ahimsa.
• A Jain should try to fulfill national responsibility through non-violent service instead.

If you want, I can also explain this from the Shwetambar and Digambar perspective separately.