Best way to redirect multiple urls?

I have a site with about 50 urls that need to be changed permanently.
Example from mysite.com/day_swimming.htm to mysite.com/day-swimming.html
What is the fastest way to do this?
Thanks in advance.

 

RedirectPermanent /day_swimming.htm http://www.mysite.com/day-swimming.html
RedirectPermanent /this_url.htm http://www.mysite.com/a_new_url.html
RedirectPermanent /that_url.htm http://www.mysite.com/another_new_url.html

Code (markup):

will do the job.

If the point is to replace unchanged.htm by unchanged.html, there is an easier solution with:

RewriteEngine on
RewriteRule ^(.*)\.htm$ http://www.mysite.com$1.html [L,R=301]

Code (markup):

Jean-Luc

 

Cheers for that. Yeah I need to change the underscores to hyphens also.
So I just add those lines to my htaccess. ok now to busy with it