There were 62 boats built of the Los Angeles Class nuclear powered, attack submarines. The last 23 boats in the class feature improvements such as better quieting and a more advanced combat system. They are known as "688i" boats. The most obvious improvement is relocating the forward diving planes off the sail and onto the hull. This placement is better suited to under ice operations. As of the date of release of this print, 42 Los Angeles Class submarines are still in active service. 20 have been retired as the new Seawolf and Virginia Class submarines are added to the fleet.