The Combined Defence Services referred to as CDS Examination. The Combined Defence Services is conducted twice a year by the Union Public Service Commission. CDS Examinations conducts for recruitment for the Indian Military Academy, Officers Training Academy, Indian Naval Academy, and Indian Air Force Academy. The graduates who are unmarried, are eligible to sit for the exam. Successful candidates are admitted into the respective Academies after an interview conducted by the Services Selection Board (SSB). The Notification for the examination is usually released in the months of October and June, and the examinations are conducted in February and November respectively. The age limit for Indian Military Academy, Air Force Academy, Naval Academy is 19-24 years and for Officers Training Academy it is 19-25 years.
The syllabus for the Combined Defence Services (CDN) is available here, you can get it from the link given below.