Planning against strong Japanese ASW

British planners did not assume a T-class boat would face a conveniently weak escort screen. Royal Navy experience with Japanese forces in the First World War encouraged a demanding estimate of future Japanese anti-submarine warfare. Intelligence officers, constructors, and planners allowed for the possibility that an opponent might pursue a technology Britain had dismissed and make it work. That institutional caution appears inside the submarine as duplicated diesel engines, electric motors, and shafts. The redundancy gave the boat alternatives when machinery failed and matched a broader design preference for preparing against unexpected enemy or system performance.