ACLS is the initialism for Automatic Carrier Landing System. For more, see http://thanlont.blogspot.com/2011/07/look-no-hands.html
Up until now, I'd never seen a good picture of the radar reflector as incorporated on the F-4 Phantom although I'm sure there must be one or more in the F-4 books that I don't have. This was the best I could come up with. There was a door under the nose and a corner reflector extended from the compartment it was housed in.
Thanks to Angelo Romano, we now have one: