Applying for British Passport

My question is what documentation would be needed for applying for a British Passport.
I was born in England, my mother was a British Citizen who married an American Military Man (my dad). As far as I understood I had dual citizenship without a British Passport but an American one. I have my birth certificate but have no idea where my mother is (could be alive or dead, I don't know) have not seen her in 35 years. My father just passed and not sure where to go from here.
I have family in the U.K.
Thank You

What year were your born?

you are British citizen because you was born in the UK before 1983 and of course because your mother is British. anyway you need to present your birth certificate, your parents's marriage certificate and your parents's ID as a support documents for your application. But what I understood now is you do not know where is you mother now and of course you will not be able to present her ID so I hope someone from the experts here will help you, or you can contact the British Consulate in your country to ask them about this issue.

I was born 1968 and thank you for the quick reply. Documents may be a bit sticky but hope it will go well.
Thanks again Cheers

You can buy the documents (birth and marriage certificates) from the gro.gov webiste and they will post certified extracts to you.