Formation and affiliation bonuses
Ships that work together with other ships over time will gain a bonus to their effectiveness. Adding new ships will upset the balance for a while, until the new ships can be properly integrated.
This applies to squadrons (i.e. escorts), divisions (i.e. capital ships), and task forces (capitsl w/escorts).
Example: The destroyers of Lion's Pride gain a squadron bonus when operating together.
Example: The cruisers of 2nd CruDiv gain a division bonus when operating together.
Example: BatDiv 1 and Fuires Sqd gain a TF bonus when operating together.
Ships from the same affiliation also gain a slight bonus when operating together. If ships from hostile affiliation are placed together it will likewise hamper the formation.
Example: The ships that came with Admiral von Graves gain a bonus when working together.