China's primary conventional attack submarine with indigenous Stirling air-independent propulsion — a quiet, multi-week-endurance boat built for regional sea denial, and the platform behind Beijing's push into the submarine export market.
Russia's troubled Project 677 diesel-electric attack submarine — a mono-hull design intended to replace the Improved Kilo with Kalibr capability and planned air-independent propulsion, but plagued by decades of delays and an absent AIP system.
Russia's diesel-electric Kalibr-capable attack submarine — the "Black Hole" of the Black Sea, a widely exported SSK and the platform behind the only documented submarine-launched cruise-missile strikes in combat.
A Franco-Spanish diesel-electric attack submarine family with optional MESMA air-independent propulsion, exported to Chile, Malaysia, India, and Brazil, and the backbone of India's Kalvari and Brazil's Riachuelo classes.