What would have made the Type 21 and Type 23 workable modular designs?
Short answerContinuous module production and a rigidly enforced standard interface.
NotesThe proposed remedy is to keep factories producing modules to an actual standardized system. That standard must be enforced rigidly. The failure identified for Type 21 and Type 23 is the inability to sustain that discipline. Calling a design modular does not by itself keep the production system standardized.