Essentially you are missing apple decision to make discovering the link as difficult as possible, without actually making it impossible.

I don't play the apple game. I do not pay the extra to have the i in my devices. So everything I say has to be rather link oriented.

This link which a about a month old looks like it offers the answer. It talks about linking to google calendar, but the URL you need is the same

Thanks for the reply. But no, I was much less clever than that. I had a link from my university calendar and didn't know how to add a new calendar, all I could find was import & export and thought that was how it worked. So in case there is anyone out there is as basic as me and need to add an online calendar to their Thunderbird.

1) In thunderbird, open your calendar. 2) On the left hand side beneath the tiny calendar it says calendar. There is a little plus sign to the right of that. click it. 3) choose on the network 4) there is now a place to put your url, so go ahead and do it