HELP: Multiple sites on one host

Good day,

I have a website that I am required to update. It is a website for one company that requires a separate section on the website for each department. So the opening page will show the company, and then the person selects which department they want to view and it opens a whole website. Looking to recreate 3 departments on the one website with the one hosting site. Each department will look completely different from each other, have similar layouts, and each have its own picture gallery.

I already have the two departments done in normal html a while back, but want to know if it is easier to just add the new one in wordpress, or re-create the whole website in wordpress? Don’t even know how to create the first page as all wordpress themes have the whole page loaded, while i need to create the intro page, before loading the 3 different departments.

Any ideas or options to approach this problem will be highly appreciated.

Many Thanks
Kavir