CDS Full Form: Combined Defence Services Exam Complete Guide
CDS stands for Combined Defence Services. The Combined Defence Services Examination is conducted by UPSC twice a year as a gateway to four Officer Training Academies of the Indian Armed Forces: Indian Military Academy (IMA), Indian Naval Academy (INA), Air Force Academy (AFA), and Officers’ Training Academy (OTA).
Unlike NDA, which targets Class 12 students, CDS is for graduates. If you’ve completed your bachelor’s degree and want an officer’s commission in the armed forces, CDS is your primary route.
CDS Full Form and What the Exam Covers
The Combined Defence Services Examination is “combined” because a single exam serves as the written filter for multiple defence academies and services. You appear for one exam, clear it, and then choose your academy based on your preference and merit.
UPSC conducts CDS I (notified in October/November, held in February) and CDS II (notified in May/June, held in September) every year.
Four Academies Under CDS
| Academy | Full Name | Location | Service |
|---|---|---|---|
| IMA | Indian Military Academy | Dehradun, Uttarakhand | Indian Army |
| INA | Indian Naval Academy | Ezhimala, Kerala | Indian Navy |
| AFA | Air Force Academy | Dundigal, Hyderabad | Indian Air Force |
| OTA | Officers’ Training Academy | Chennai, Tamil Nadu | Indian Army (Short Service Commission) |
IMA, INA, and AFA lead to Permanent Commission (PC) — a full career in the armed forces. OTA leads to Short Service Commission (SSC) — initially 10 years (extendable to 14 years), with the option to apply for PC during service.
OTA also has a separate women’s division in Chennai for SSC (Women Non-Technical).
CDS Exam Pattern
The CDS exam has different paper structures for IMA/INA/AFA versus OTA.
For IMA, INA, and AFA
| Paper | Subject | Questions | Marks | Duration |
|---|---|---|---|---|
| Paper I | English | 120 | 100 | 2 hours |
| Paper II | General Knowledge | 120 | 100 | 2 hours |
| Paper III | Elementary Mathematics | 100 | 100 | 2 hours |
| Total | 300 | 6 hours |
For OTA (Men and Women)
| Paper | Subject | Marks | Duration |
|---|---|---|---|
| Paper I | English | 100 | 2 hours |
| Paper II | General Knowledge | 100 | 2 hours |
| Total | 200 | 4 hours |
OTA candidates don’t write Mathematics. This makes OTA slightly more accessible.
Negative Marking
Like all UPSC exams, CDS has negative marking: one-third of the marks assigned to a question are deducted for each wrong answer. Don’t guess blindly.
Nature of Questions
- English: Reading comprehension, grammar, sentence correction, ordering of sentences, vocabulary
- General Knowledge: Current events, history, geography, Indian polity, economy, science (basic Physics, Chemistry, Biology)
- Mathematics: Arithmetic, algebra, trigonometry, geometry, statistics — up to Class 10 level only
The Mathematics paper for CDS is limited to Class 10 standard. But don’t underestimate it — accuracy and speed matter, and the breadth of topics requires solid fundamentals.
CDS Eligibility: Who Can Apply
Eligibility varies by academy. This is where many aspirants trip up.
| Academy | Educational Qualification | Age | Marital Status |
|---|---|---|---|
| IMA | Bachelor’s degree (any discipline) | 19–24 years | Unmarried |
| INA | Bachelor’s degree in Engineering OR B.Sc. with Physics/Mathematics | 19–24 years | Unmarried |
| AFA | Bachelor’s degree with Physics and Mathematics OR BE/B.Tech | 20–24 years | Unmarried |
| OTA (Men) | Bachelor’s degree (any discipline) | 19–25 years | Single/married/divorced |
| OTA (Women SSC) | Bachelor’s degree (any discipline) | 19–25 years | Single/married/divorced/widowed |
Key differences to note:
- INA and AFA require Physics and Mathematics at degree level
- OTA allows married candidates (for both men and women)
- AFA age limit is 20–24, slightly different from IMA/INA
Physical Standards
Like NDA, CDS candidates must meet physical standards:
- Minimum height: 157.5 cm for Army, 157 cm for Navy, 162.5 cm for Air Force (men)
- Minimum height: 152 cm for women
- Corrected vision requirements vary by service and branch
Medical standards are assessed at the SSB interview stage by service medical boards.
NDA Full Form: National Defence Academy Complete Guide
SSB Interview: The Real Test
Like NDA, the CDS written exam is only a qualifying filter. The SSB (Service Selection Board) interview is where selection actually happens. Written exam marks don’t count toward your final merit.
SSB Structure: 5 Days
Day 1 — Screening Stage:
- Officer Intelligence Rating (OIR) — verbal and non-verbal tests
- PPDT (Picture Perception and Discussion Test) — candidates view a vague image, write a story, then discuss in groups
- Only those who clear Day 1 continue. Others are sent back home.
Day 2 — Psychological Tests:
- TAT (Thematic Apperception Test) — write stories for 11 images
- WAT (Word Association Test) — write first thought for 60 words, 15 seconds each
- SRT (Situation Reaction Test) — write responses to 60 situations in 30 minutes
- Self Description Test — write what you think of yourself, what your parents/teachers think
Day 3–4 — GTO (Group Testing Officer) Tasks:
- Group Discussions (2 rounds)
- Group Planning Exercise
- Progressive Group Task, Half Group Task, Final Group Task — outdoor physical/problem-solving obstacles
- Individual Obstacles — 10 obstacles, 3 minutes
- Command Task — lead a small group through an obstacle (after individual interviews)
- Lecturette — 3-minute talk on a topic picked from 4 chits
Day 2–4 (parallel) — Personal Interview: The IO (Interviewing Officer) conducts a 30–45 minute personal interview covering your background, academics, interests, and officer potential.
Day 5 — Conference: All three assessors (Psychologist, GTO, IO) discuss each candidate. Candidates are called individually for a brief conference. Final selection is announced.
What SSB Assesses: Officer Like Qualities (OLQs)
SSB assesses 15 OLQs grouped under Effective Intelligence, Reasoning Ability, Social Adaptability, Communication, and Dynamism. You can’t fake these — assessors look for consistency across all tests over 5 days.
CDS Vacancies: How Many Get Selected?
Each CDS exam notifies vacancies for each academy. Typical numbers:
| Academy | Vacancies per CDS (Approx.) |
|---|---|
| IMA | 100 |
| INA | 45 |
| AFA | 32 |
| OTA (Men) | 170 |
| OTA (Women SSC) | 12–15 |
Total approximately 360–365 per CDS exam, or 720–730 per year.
About 4–5 lakh candidates appear for each CDS exam. Around 7,000–10,000 qualify the written stage and are called for SSB. The final selection rate from SSB is roughly 5–7%.
CDS vs NDA: Key Differences
| Parameter | NDA | CDS |
|---|---|---|
| Education | Class 12 (appearing/passed) | Graduate |
| Age | 16.5–19.5 years | 19–25 years |
| Commission | Permanent (all wings) | PC (IMA/INA/AFA) or SSC (OTA) |
| Training after academy | IMA/INA/AFA (1–1.5 more years) | Commissioned directly after academy |
| Rank on commissioning | Lieutenant/Sub-Lt/Flying Officer | Same |
| Exam conducted by | UPSC | UPSC |
Both exams are conducted by UPSC, but NDA is for younger candidates still in school/fresh out of Class 12.
UPSC Full Form: Union Public Service Commission Guide
Frequently Asked Questions
What is the full form of CDS?
CDS stands for Combined Defence Services. The Combined Defence Services Examination is conducted by UPSC twice a year for entry into IMA (Army), INA (Navy), AFA (Air Force), and OTA (Army Short Service Commission).
Who conducts the CDS exam?
UPSC (Union Public Service Commission) conducts the CDS written examination. The SSB interviews and medical examinations are conducted by the respective armed service Selection Boards.
What is the age limit for CDS?
Age limit varies by academy: 19–24 years for IMA and INA, 20–24 years for AFA, and 19–25 years for OTA (both men and women’s entry). All ages are calculated based on the date of commencement of training at the academy.
Is Mathematics required for CDS OTA?
No. OTA entry (both men’s and women’s) requires only English and General Knowledge papers. Elementary Mathematics is required only for IMA, INA, and AFA entry.
Does the CDS written exam score count for final merit?
No. The written examination is only a qualifying filter to shortlist candidates for SSB interviews. Final merit is based entirely on SSB marks. Candidates with higher written scores don’t get any advantage in the final selection.
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