Israel's Dolphin-class submarines — German-built diesel-electric attack boats with air-independent propulsion, a reported nuclear second-strike role, and a history wrapped in operational secrecy that only occasionally lifts.
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.
Germany's pioneering fuel-cell AIP attack submarine — the ultra-quiet Type 212A, now evolving into the larger Type 212CD for North Atlantic/Arctic operations, operated by Germany, Italy and (on order) Norway.