Hello Aspirant,

After doing a Bsc. Nursing course:

You may join the Indian Army as Short Service Commissioned officers in the Military Nursing Service. The eligibility is is pass in MSc (Nursing) /PB B Sc (Nursing)/B Sc(Nursing) from INC recognized University and be a registered Nurse and Midwife from a State Nursing Council (You will be required to submit the original and self attested copies of marksheet, passing certificate and valid State Registration certificate at the time of interview). You can get clear information regarding this by visiting their official website.

After 12th:

To join the Nursing College at Armed Forces Medical College where they will undergo BSC in Nursing under military discipline and after which you will be appointed as Nursing Officers with pay scale of nursing officer.For Army Bsc.Nursing , the eligibility is pass in class 12th or equivalent examination in the first attempt (12 years schooling) with Physics, Chemistry, Biology, and English as mandatory subjects. The minimum pass percentage required is 55%. Students in their final year of schooling can also apply. After clearing a written examination , you will be called for interview and medical examination.

https://medicine.careers360.com/articles/indian-army-bsc-nursing-application-form

All the best