hmmm...KM subs? SS1 and SS2 are still kinda slow.
Get a good engineer, get a lot of vets on the sailors, and cut rookie sailors to save weight. French and US subs can be quick too.
Overall though, all SS1 and SS2 are on the slow side. At-level sailors simply do not have the engine ability to increase speed by much, nor the displacement to carry high level sailors.