While the title on the cover is "The Underwater Raiders", the title on the story itself is "The Underwater Foes".
This story uses the Western-created scientist mouse "Professor Theorem" and a generic, leaderless bunch of cats who seem to be using a citadel and technology that they just stumbled upon. The story almost cries-out for the characters that populated the St. John era Mighty Mouse continuity, such as scientist mouse "Professor Edam" and cat villains "The Claw" and "Professor Ohm". Those characters would appear at Western shortly thereafter in the Western reprints of St. John material seen in Mighty Mouse #161-165 (1964-1965), presumably indicating there was no prohibition on using such characters.
The positioning of Mighty Mouse's arms and hands suggests that he is holding-up or otherwise stopping something or someone - indicating that this illustration of Mighty Mouse was lifted from another Western source.
Illustration shares back cover space with logo and ad copy for whichever firm is distributing the issue as a giveaway premium. Illustration comprises top third of page, lower two thirds can be blank if no named sponsor.