Defence Minister Rajnath Singh presided over the quiet commissioning of INS Aridhaman (S4) , the third indigenously built SSBN of the Arihant‑class , at Visakhapatnam on 3 April 2026 . The vessel strengthens India’s nuclear triad and falls under the Strategic Forces . Key Developments Commissioning of INS Aridhaman (S4) confirmed by the Defence Minister’s cryptic tweet. Commissioning coincided with the induction of the stealth guided‑missile frigate INS Taragiri . Project executed by the Ship Building Centre (SBC), Visakhapatnam. Aridhaman (S4) and the upcoming S4* (potentially named Arisudan ) are larger (≈7,000 t) than earlier boats (≈6,000 t). Important Facts Aridhaman can carry up to 24 K‑15 Sagarika missiles , or eight K‑4 missiles , or future K‑5 missiles , all nuclear‑capable. Earlier SSBNs – INS Arihant and INS Arighaat – could carry about 12 K‑15 or four K‑4 missiles. K‑15 Sagarika missile range: ~750 km. K‑4 missile range: ~3,500 km. India joins the United States, Russia, China and France as a nation with a credible nuclear triad. Indigenous development of SSNs is underway, with at least two expected by 2036‑2039 . UPSC Relevance The commissioning underscores India’s strategic autonomy in defence production (GS2) and its commitment to a credible second‑strike capability, a core topic in GS3 – Security & Defence . Understanding the technical specifications of SSBNs, missile ranges, and the role of the Strategic Forces helps answer questions on nuclear doctrine, deterrence, and maritime security. Way Forward Complete sea‑trials and induction of the S4* (potentially Arisudan ) to further augment sea‑based deterrence. Accelerate indigenous development of advanced SLBMs (e.g., K‑5) to extend strike range. Expand the indigenous SSN programme to ensure a balanced submarine fleet for both strategic and conventional roles. Strengthen the Ship Building Centre infrastructure to meet future production targets.