Why submarine totals cannot be judged without context

Would 50 Astute-class submarines sensibly replace a much larger mixed nuclear and diesel-electric fleet?

There is not enough information; fleet totals are meaningless without the missions, threats, infrastructure, and costs involved.

The proposed fleet of 50 Astute-class submarines would replace a much larger mixed nuclear and diesel-electric force. Platform totals alone cannot support a verdict. Strategic circumstances, likely threats, required missions, infrastructure, and affordability would determine whether the smaller fleet was sensible. Force planning is not reducible to arithmetic.