What career path must one follow to become a captain of a cruise ship, cargo ship, or oil tanker?

Captaincy is not a scholastic qualification. It is a position earned by qualifications and experience.

The first thing you would want to do is get your helmsman accreditation, (or boatswain or whatever you want to call it). Most licensing authorities have different grades of licensing for different classes of boats/ships.

Once you have this, you would have to secure employment as a helmsman or navigator or such. Then it is just working your way up the ranks/heirarchy to get captaincy of your own ship.

On the other hand... if you own the boat/ship, I guess that would automatically make you the captain.

If you're interested in getting into maritime careers, I'd recommend contacting a maritime college, or check in with your local further education establishment.

It takes 4 years to get through either program.
You graduate an officer but not a captain. You will
need a few years at sea before you gain your captains
license.

You have to be able to do flipses of the top deck.Once you have mastered the flip off the top deck,you are good to go

One of the main points in gaining a ' captaincy' is experience. You may be very intellectual with a good memory and know ALL the written side of the qualifications, but most maritime authorities demand sea time experience, This can only be gained through practical employment. An example in Australia is vessels with SPV [ Surveyed Passenger Vessel]. You may be a billionaire, able to afford the most expensive vessel [ Greg Norman's ship cost 80 million, built in Western Australia] but without the proper accreditation of a 'commercial' skipper, gained through schooling and 'sea time' , would not be allowed to operate a twenty foot SPV. It does take time, and most authorities specify the time required. You simply cannot get around this requirement.

attend a state maritime school like ny's fort schuyler or federal
maritime at kings' point on longisland ny.