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One can fulfill his dream of joining officer cadre of Indian armed forces after 12th , one can join army, airforce and navy after completing 10+2 by various entries, but there are certain eligibility criteria which is to be fulfilled. Below is a detailed view of how one can join India armed forces after 12th.
Army
There are two 2 ways of joining Indian Army after 12th:
1. NDA & NA Examination :
The NDA entry is open twice a year.
Form availability Mar and Oct Notified by UPSC
Vacancies Per Course 300 (195 Army, 66 Air Force, 39 Navy)
The requirements for entry into NDA is as follows:
Age 16 to 19 yrs(at the day the course is expected to begin)
ie. Born Between 2nd Jan to 1st Jul for Dec Course and 2nd Jul to 1st Jan for Jul Course
Qualification 12th Class of 10+2 for Army and with Physics and Maths for AF/Navy
Marital Status Unmarried
Application to be Received by 10-15 Nov for Jan Course and 10-15 Apr for Jul Course
Likely SSB Date Sep to Oct and Jan to Apr(SSB can sometimes get very delayed, so this is just for reference)
Date Commencement of Training Jan and Jul
Training Academy NDA , Khadakwasla, Pune
Duration of Training 3 Yrs at NDA and then 1 Yrs at IMA, Dehradun
2. Technical Entry Scheme -TES(For High School Science Graduates):
The TES entry is open twice a year.
Vacancies Per Course 85
Form availability Apr and Sep Notified by Additional Directorate General of Recruiting
The requirements for entry into TES is as follows:
Age 16 to 19 yrs
ie. Born Between 1st Jul to 1st Jul for Jan Course and 1st Jan to 1 Jan for Jul Course
Qualification 10+2 Physics, Chemistry & Maths (aggregate 70% and above to apply)
Marital Status Un Married
Application to be Received by 30 Jun and 31 Oct
Likely SSB Date Aug to Oct and Feb to Apr
Date Commencement of Training Jan and Jul
Training Academy IMA Dehradun
Duration of Training 5 Yrs (1 Yrs IMA & 4 Yrs CTWS) Permanent Commission after 4 Yrs
Airforce:
Only one way:
1. NDA & NA Examination : You can join NDA by taking the exam conducted by Union Public Service Commission (UPSC). This exam is conducted twice a year in all major cities throughout India.
Eligibility Criteria
Age 16 to 19 years(at the time of commencement of course)
Nationality Indian
Gender Men only

As a minimum criterion of eligibility, candidates seeking admission to the course need to have completed the 10+2 or equivalent level of education from a recognized educational Board, and in the Commerce stream, with Accounts, Math, Business, and Economics as main subjects, and a minimum aggregate score of 50%.
Ideal students of the course would possess the following skills:
1) Interest in and aptitude for technology, Mathematics, and Science.
2) Familiarity with programming and computer hardware/software.
3) Competent knowledge of core electrical and computer subjects such as electronics, electrical systems, computers, circuits, design and modelling.