Lower ranks are in general easier to obtain. The higher you go the more missions you'll have to do before seeing "naval progression" missions.
Your best bet, and that's how i got to rank of knight is: go to a minor faction, build up your rep with them doing missions or turning in bountys/explore data, wait for naval progression mission. Than move to another minor faction and repeat the same. I find it hard to get several naval progression missions from the same minor faction.
Your best bet, and that's how i got to rank of knight is: go to a minor faction, build up your rep with them doing missions or turning in bountys/explore data, wait for naval progression mission. Than move to another minor faction and repeat the same. I find it hard to get several naval progression missions from the same minor faction.