"The Avengers Meet Sub-Mariner!"
The Hulk has stormed off, and the Avengers feel that he is now their responsibility. They consult with the Fantastic Four, X-Men, the Teen Brigade, even Spider-Man, but fail to find the Hulk before the scheming Sub-Mariner does. Namor convinces the Hulk to stand in an alliance against the Avengers, but the deal is short-lived. 25 pages (X-525).
Reprinted in Marvel Super-Heroes (1967) #21.
Note: title taken from the splash page and not the cover.