The Russian Oscar-class nuclear-powered guided-missile submarine, also known as an SSGN, is one of the most fearsome adversaries a carrier strike group could face. When one goes out to sea, NATO dedicates a lot of assets to finding it. Why? It may have something to do with the fact that an Oscar-class submarine packs 24 SS-N-19 Shipwreck cruise missiles, which can go Mach 2 and pack a 1,000-kilogram warhead (or a nuclear warhead), in addition to powerful 650mm torpedoes.
NATO spent a lot of time tracking Oscar-class submarines.
The United States has never had a true counterpart to the Oscar. Four Ohio-class nuclear-powered ballistic missile submarines (or SSBNs) were modified to pack 154 Tomahawk cruise missiles each, but the Tomahawks in question are land-attack missiles. Furthermore, these submarines, to some extent, still operate like the "boomers" they were, often finding a spot to park their very powerful arsenal.
USS Georgia (SSGN 729) is one of four Ohio-class submarines converted to carry BGM-109 Tomahawk cruise missiles.
(US Navy photo by Mass Communication Specialist 1st Class James Kimber)
This is because, when it comes down to it, the SSBN isn't exactly intended to sink an enemy ship. Yes, they carry torpedoes, but those are only for self-defense. Their real purpose is to keep 24 UGM-133 Trident II D-5 ballistic missiles, each loaded with as many as 14 375-kiloton W88 nuclear warheads, safe and ready for use.
Well, those Ohios are getting old and now, there's a need to replace them. What this also means is that the U.S. Navy will soon have a true answer to the Oscar in the form of the Block V Virginia-class nuclear attack submarine. According to a handout obtained at the SeaAirSpace 2018 expo in National Harbor, Maryland, these subs will be somewhat longer than the earlier Virginia-class due to the addition of a plug that will hold 28 additional Tomahawks. Since some Tomahawk variants are capable of targeting ships, this makes the Block V Virginia-class sub a more versatile SSGN than the Oscar was.
A 2012 Congressional Budget Office report indicated the Navy planned to buy 20 of these submarines. With the increase in defense budgets in recent years, however, there's no telling just how high that total can go.