From January 1975 (so it would have been on sale during the last few months of the previous year): the launch issue of Marvel's American black & white mag UNKNOWN WORLDS OF SCIENCE FICTION.
These mags were shipped across the Atlantic (and subject to the sane erratic distribution) alongside the colour books and were another reason why the first few years of the British Bullpen focused strictly on traditional weeklies rather than rolling out a variety of frequencies and formats to see which performed best.
But they also supplied useful reprint fodder for the early hard-to-fill British SF outings PLANET OF THE APES and STAR WARS WEEKLY. The formulas, and licensing restrictions (no BATTLESTAR GALACTICA or STAR TREK in SWW) often left much of the Marvel inventory off limits and occasionally (usually through mergers) created some tenuous combinations (scare-fare in POTA or Conan in FUTURE TENSE) just to keep the pages filled and the presses rolling.
Canny Marvel management made their lives easier (and their margins fatter) by quietly making each issue of STAR WARS WEEKLY eight pages lighter, for the same cover price, as its easier to fill contemporaries. The US magazines proved a useful source of filler whilst Marvel New York ratcheted up their SF offering (allowing Marvel UK to publish FUTURE TENSE in 1980-81: essential a compendium of SWW supporting features belatedly anchored by STAR TREK's return to a British weekly after a five year 'away mission').
Six issues of UNKNOWN WORLDS shipped on a bimonthly schedule during 1974 with a further one-shot the following year. This first issue consisted of a lot of non-Marvel commissions that had originally appeared in other magazines or fanzines. The amount of new material increased for the remainder of the run. Adaptations of literary work was often accompanied by interviews with their authors.