I am still somewhat confused.

I just finished a game. it was a pretty long game and I had the opportunity of researching a lot.

What I usually do is research shilds and phasors. I usually get 2 different typs of ships. What I am wondering about is what's the point of researching heave weapons like plasma and all the others further down the tech tree if none of my ships can get them?

Or am I missing something completly? Is there a way to get the powerful weapons on some of my ships that I have already produce?

I guess the manual is not that clear...

If somebody could walk me through that I would be greatful.

Thanks