good to see that you have a great zeal for your future and you have started thinking about it in your study time only .
Its really good as you will overcome many obstcales which may come on your way while making your career choice.
As you are from engineering,you have even great scope as Indian navy really needs good and skilled engineers for managing the work and you seems to be really interested in joining Indian defence.As an engineer you have following choices.
SSC (Technical men):SSC means Short Service Commission.
The eligibility criteria is as follows:
1. Indian Citizen
3.Having B.Tech degree with atleast aggregate 60%
4.Age limit :19.5 to 25 years