An alien ship comes to 14th century Earth, and makes the mistake of landing where there is a clever pommie ruler and his own highly competent military force.
They lose, lose their ship, and the poms are off to the alien planet to take it over instead!
The not too bright sheepish aliens don't do very well, despite technological superiority:
"Nonetheless, dogged almost as Englishmen, they ran on to our very wall. And here our common men-at-arms stood to receive them. The women fired and fired, pinning down a goodly part of the foe. Those who came so close that guns were useless, must face axe, spear, billhook, mace, morningstar, dagger, and broadsword.
Despite their awesome losses, the Wersgorix still outnumbered our folk two or three to one. Yet it was scarcely fair. They had no body armor. Their only weapon for such close-in fighting was a knife attached to the muzzle of the handgun, to make a most awkward spear ... or the gun itself, clubbed. A few did carry pellet-firing sidearms, which caused us some casualties. But as a rule, when John Blueface fired at Harry Englishman, he missed even at pointblank range, in all that turmoil. Before John could fire again, Harry had laid him open with a halberd."
The poms learn fast, and soon it is Galactic Empire time, of necessity.:
3.5 out of 5
OSR Tools in the Super Hero Setting
54 minutes ago