The Kilo's enduring value rests on acoustics rather than performance. A conventional boat running on batteries in shallow, acoustically cluttered water - the Baltic, Black Sea, Persian Gulf, South China Sea - is a genuinely difficult target, which is why the class earned its "Black Hole" reputation and why it sold to India, China, Vietnam, Algeria and Iran. That reputation should be read carefully: it describes a well-handled boat operating submerged in favourable conditions, not an inherent immunity. The design dates from the 1970s, lacks air-independent propulsion, and must still snorkel, which is when it is most detectable.
What changed the class's strategic weight was the Kalibr missile. Project 636.3 turned a defensive coastal submarine into a mobile land-attack platform, and Russia used that capability against Syria from 2015 and against Ukraine from 2022. A handful of relatively cheap conventional boats able to hold targets hundreds of kilometres inland at risk is a disproportionate return on investment, and it is the main reason the Black Sea Fleet's submarine force remained militarily relevant after its surface ships were pushed out of the western Black Sea.
The counterpoint is the loss of Rostov-on-Don. Struck by cruise missiles in September 2023 and sunk at Sevastopol in August 2024, it demonstrated that a submarine's survivability advantage disappears alongside a pier, and Ukraine has since pressed the point with an uncrewed underwater vehicle attack on another Improved Kilo at Novorossiysk in December 2025. The lesson is about basing rather than the design: quietness at sea does not compensate for a base within reach of precision strike, and navies operating Kilos in contested littorals face the same exposure.
