This has three phases (Conceptual, Preliminary and Final);
KEEL LAYING (or laying down the first hull section);
BUILD (now often called Modular Build)
Since 1993, all submarines have been built as hull units undercover at Barrow and welded together to form the hull, supported on stands in the covered Build Hall;
ADVANCED OUTFITTING
In modern submarine building, as much outfitting as possible and some systems testing is actually completed before the hull units are welded together (closed up);