Akula Submarine: Toshiba Milling Machines, the Nerpa Fire and INS Chakra

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When the first Project 971 attack submarine was launched in 1985, Western intelligence believed the Soviet Union was a decade away from that level of quiet. NATO called it the Akula, Russian for shark, though the Soviets called the project Shchuka-B and used Akula for the boats NATO named Typhoon. The design wraps a titanium or high-yield steel pressure hull inside a lighter outer hull shaped for flow, giving it large ballast tanks and extra reserve buoyancy. A teardrop pod atop the rudder holds a towed sonar array, and the boats carry four 533mm and four 650mm tubes. The SOKS system uses hull sensors to detect the warm water and salinity changes left in another submarine's wake.

Much of the quiet came from the Toshiba-Kongsberg scandal: in 1983 and 1984 Toshiba Machine illegally sold four nine-axis milling machines to the Soviet Union, run by Norwegian Kongsberg controls, allowing propellers that avoid cavitation. U.S. officials estimated countering the result cost $30 billion. The Akula II Vepr, commissioned in 1995, was quieter than improved Los Angeles class boats, and the only Akula III, Gepard, was commissioned in 2001 with Vladimir Putin present, a year after the Kursk sank. In 1996 the Tigr tracked a U.S. Ohio class submarine on patrol, two Akulas operated off the U.S. East Coast in 2009, and in 2012 one was reported in the Gulf of Mexico for over a month.

• In 2008 a halon fire system misfired on the Nerpa during trials in the Sea of Japan, killing 20 people, 17 of them civilian technicians.
• India commissioned the repaired Nerpa as INS Chakra in 2012 under a lease.
• Missile Technology Control Regime limits capped Chakra's Club-S missiles at 300 km, versus about 3,000 km for Russian land attack missiles.
• After the 2019 Balakot strikes, India sent Chakra to hunt the Pakistani submarine PNS Saad.
• Chakra returned to Russia a year early in June 2021 over reactor maintenance, and a $3 billion follow-on lease slipped to at least 2028.