Decrease Units Speed

I dont want to use delay , I want to my units travel slower so I can go sleep

for example you have destroyers and aircraft carriers on sea

first point have destroyers

second point have destroyers + aircraft carriers

third point have destroyers

you have units at 3 points , and you want all of them move same speed even they are different units if I send them together and enemy attack , my carriers will get damage and I don't want it , I want to send them with 3 groups and carriers will move their between but destroyers always faster than carriers