The Akula nuclear-powered attack submarine was first introduced by the Soviets in 1986. There are 4 sub-classes as follows:
The "original" 7 Akula I submarines, K-284, K-263, K-322, K-480, K-391, and K-317.
Six "improved" Akula I submarines, K-461, K-328, K-419, K-154, K-295, and K-152.
One Akula II submarine, K-157.
One Akula III submarine, K-335.