The Alfa class was the Soviet submarine class famous for exceptional speed and titanium pressure hulls.
Known in Soviet service as Project 705 Lira, Alfa-class submarines were designed as compact nuclear-powered attack boats. Their titanium alloy pressure hulls reduced weight while allowing operation at considerable depth. A liquid-metal-cooled reactor helped provide very high acceleration and speed.
The boats could reportedly exceed 40 knots, making them among the fastest operational military submarines ever built. Their automation also allowed them to operate with unusually small crews. These advantages came with demanding maintenance requirements and a relatively short service life.
Alfa is often confused with the larger Typhoon class, which was built for strategic ballistic-missile missions. Alfa boats were attack submarines, intended to hunt enemy submarines and surface ships rather than carry intercontinental ballistic missiles.