VIRGINIA-CLASS ON THE SURFACE: The U.S. Navy attack submarine USS Delaware conducts sea trials in the Atlantic Ocean. Photo taken August 31, 2019. This How to Make War “Submarines” post from 2014 discusses the USN’s modification program for its Virginia-class nuclear attack subs.

Each new batch of the Virginia SSNs have new features. In April 2014 the U.S. Navy ordered ten Block IV Virginia class at a cost of $1.8 billion each. These are to be delivered at the rate of two a year through 2018. This is the largest submarine order (in terms of dollar value) in U.S. history. There are already eleven Virginia’s in service and seven more Block IIIs under construction or on order. This new order is long-term, which is rare, but it results in lower prices because components can be ordered in larger quantities and farther in advance.

The post provides an excellent summary of the process as well as the technical details.