Avengers #40

"Suddenly...the Sub-Mariner!"

Roy Thomas writer
Don Heck penciler 
George Bell inker 
Sam Rosen letterer    

essentially, Namor finds the Cosmic Cube and figures out how to use it, and the Avengers, plus Hercules have to stop him.  I believe this is historic for the being the first time Hercules and Namor have met.  I have to believe that Herc would have mopped the floor with the Sub-Mariner.  It would have been cool if Herc had dropped the fact that he is on a first name basis with Poseidon/Neptune, since that's someone that Namor has met in the past as well.
Wanda has a dizzy spell, so Pietro stays with her in this adventure.  Cap, who is battling the Red Skull warns the Avengers about the Cosmic Cube (Tales of  Suspense 80-81 are taking place at this very same moment in the MU.  it's an all action story, and a lot of fun.

the ending is kind of interesting as well.  I'm not a fan of the Cube at all, it's a ridiculous concept even for comic books.

next- Diablo and the Dragon Man!