If these values could be added (prefferably one each for nations Navy/Airforce/Army) then so much more could be modelled. Like the Kriegsmarines struggle to expand many times over in a very short time or the IJN Airforce problems to train replacement pilots (At least for its land based aircrafts if not CVs somehow could be flagged as aircrafts/airforce too in this aspect).Regarding the training time issue, what is really missing is some resource quantity for the "training capacity" - basically the number of experienced officers and (especially) NCOs that can be spared to train the new influx. I have some ideas, but I'm still thinking through how to handle it; it's not a complete disaster the way it stands, but there may be an elegant way to do better...
Perhaps the training for each branch could have an upkeep cost of oil/supplies/money and result in a modified experience value derived from the base xp value from slider. If possible this cost should also be effected by reinforcements needed, construction & by size of force. Pretty complex stuff to figure out in a good way, must be even harder to code and balance.
Not sure how it could affect production though, the most intuitive way Imo is increased buildtime but unchanged buildcost in ICdays. Or the slightly more complex method suggested by Cueball effecting it through gearing.