According to toonzone.net:
"The X-Men's introduction to animation was inauspicious. They didn't even refer to themselves as the X-Men. Instead they opted for Allies for Peace!
The original X-Men line-up appeared in an episode of the 1966 Sub-Mariner show from The Marvel Super Heroes, the first part of which was called "Dr. Doom's Day". The story was essentially an adaptation of a Fantastic Four story, but since Grantray-Lawrenece didn't have the rights to the FF characters, they substituted the X-Men.
Oddly, the X-Men are never referred to by that name, instead known only as the Allies for Peace! The characters kept their original looks and individual names from the comics though."
The Allies for Peace can be seen after 1:30 in this clip from the episode: