I am talking about in modern day... with no pressure of rushing into a war that was already started. After a new warship, lets say a destroyer or a frigate was just commissioned, how long will it take for the ship to become battle effective? That is, how long will it take to have the ship's crew fully trained to battle ready level? By the way, is the ship crews' skill transferable? For example, if they have served on other older warships, and now it's replaced by new and more advanced warships, will their previous skills/experience be useful at all? Or do they require total retrain due to the completely upgraded/or even totally new and different systems onboard?