If you are diving into the original run with the First Doctor (William Hartnell), Season 3 followed a serial format where individual episodes had their own titles.
It was a high-stakes blockbuster special that introduced a one-off companion and set a then-record for viewership. Option 2: The Classic Era (1965) Doctor Who - Season 3Eps14
In the 2005 revival series, Series 3 officially has 13 episodes. However, streaming platforms like Prime Video and Apple TV often categorize the Christmas Special as the 14th episode. " Voyage of the Damned " If you are diving into the original run