Avengers Vol.1 #40
The Scarlet Witch collapses after the battle in the previous issue; Black Widow steals an experimental jet from General Ross; Meanwhile, the Sub-Mariner attacks a submarine destroying underwater wildlife, then decides to attack the base it came from; The Avengers receive a call from Captain America, warning that a dangerous item called the "Cosmic Cube" has been spotted near the base and the Avengers should secure it; Quicksilver stays with the weak Scarlet Witch and the Avengers arrive at the base and battle with Sub-Mariner, where Hercules unwittingly mentions the cube to him; The Sub-Mariner flees, returns with the cube and the battle starts again.
Printed: Nov 1966
Writers: Stan Lee
Art: Don Heck and George Roussos [as George Bell]
Cover: Don Heck and George Roussos