Running TMO RSRD I usually go to my patrol area pull up the shipping lane map and look for a "choke" point or convergance area close by or I look into my crystal periscope and do a little research on where IJN units were at the time.
Found the landing forces in Lingayen Gulf on 21 December 1941 just from knowing they should be there, what a sweet site it was, especially the smoke and flames against the night sky
Just remember to show up early for a good seat and wait for them.