Nuclear weapons represent the ultimate deterrence for any one world power today and, as such, many of the leasing nations have taken up local programs to ensure their own security as well as to drive national interests and patriotism. This has proven the case with India which completed its first successful nuclear detonation test in May of 1974. Since then, the nation has embraced the concept of the "nuclear triad" - that is nuclear weapons delivery by aircraft, land-based ballistic missile launchers, and submarine.
While the air component is fulfilled by the Mirage 2000 fighter-bomber and the land-based component by the Agni system, the new Arihant-class submarine has been indigenously developed for form the final point of the triangle. The group encompasses lead-ship INS Arihant (S73) and sister INS Arighat (S74) as well as two unnamed vessels still-to-some (2018). Arihant was launched in 2009, commissioned in 2016, and completed her first patrol in 2018. INS Arighat has followed and saw its keel laid down in 2010 (by shipbuilder Visakhapatnam), launched in November of 2017, and formally commissioned into service during late-2018. She is being outfitted as of this writing (2018).
INS Arighat was originally named INS Aridhaman.
The class is being built to two recognized standards: "Fleet I", which contains just lead-ship INS Arihant, and the revised "Fleet II" which includes INS Arighat and two sister ships. The latter pair are undergoing construction as of 2018. The major differences between the two fleets is additional missile cells, a more powerful nuclear propulsion fit, and slightly altered structural dimensions.
As nuclear-powered types, the class enjoys the output power and longevity of a pressurized water nuclear reactor as its primary energy source to ensure their various systems operate to maximum efficiency and the boats remain as quiet as possible. The reactor is mated to a single, multi-bladed propeller unit found at the extreme rear of the hull. Maximum surfaced speeds can reach 15 knots while undersea traveling reaches 24 knots (these figures slightly slower than leading Western designs). Because of the inherent nature of a nuclear-driven propulsion scheme, the vessel can remain at-sea indefinitely, limited only by crew fatigue and onboard food stores. The hull has an estimated test depth of 980 to 1,300 feet. Dimensions include a running length of about 370 feet with a beam measuring 49 feet and a draught down to 33 feet. The crew numbers approximately 95 personnel.
At the heart of the newer Arighat is a ballistic missile-launching capability consisting of vertically-launching cells buried in the midship section of the upper hull section. This is found just aft of the sail and consists of up to 24 x K15 Submarine-Launched Ballistic Missiles (SLBMs) which can be replaced with 8 x K-4 SLBMs as required. Beyond this the submarine has the traditional arrangement of 6 x 21" (533mm) torpedo tubes in the bow giving the vessel a multi-role attack capability.
Structurally Arighat fields a conventional design shape as submarines go: the bow is well-rounded for suitably cutting through ocean depths and the conning tower is positioned well-ahead of midships while also holding dive planes (some submarines feature their dive planes at the forward hull). The hull roof line is flat so as to better fit the vertically-launching missile bays but the sides and ventral lines of the hull are all rounded for hydrodynamics. The tailplane arrangement is of a traditional cruciform pattern with the propeller unit extended a short distance aft of this.