This was the very first suit to ever bear the bat symbol having debuted all the way back in 1939's Detective Comics #27.
The suit featured all the classic elements including the cowl, a pointed cape, a grey costume, yellow utility belt, and black trunks similar to other characters of the time period. Important to note as well is that it wouldn't have looked this way had Bill Finger not gotten involved, with Bob Kane initially keen on a garish, red and black number for the Dark Knight.