There are two sections on magic swords in JG 37 "The First Fantasy Campaign" by Dave Arneson, the first of which describes "an entire family of Magical Swords", created for use in the original Blackmoor campaign.
Daniel Boggs posted a lengthy analysis of this section in The First Magic Swords back in October, 2016, which I highly recommend. The second section was written by Arneson at a later date, and will be discussed in more detail, tomorrow.
Because these weapons are almost entities in themselves, they accrue real advantage to the figure so armed. In normal combat they merely add an extra die. It is in fantastic combat the Magical Swords are most potent. Besides allowing Elves to combat certain fantastic figures, they give a plus 1 to the dice score when employing the Fantasy Combat Table, and Magical Swords shed a light of their own over a circle 12" in diameter, which dispels darkness - but does not equal full light. Excalibur and other "Super Swords" would give a plus two or three!
For those interested in using these venerable weapons in your own campaign, check out Converting the FFC swords to OD&D.
DA1 "Adventures in Blackmoor" (1985) describes the famous "White Sword":
This powerful lawful sword +2, +3 vs. goblins, orcs, undead, and dragons has an intelligence of 12 and an ego of 12. It was forged at the command of a previous bishop to be the sword of champions and "the defense of the Church and the people" against evil. It has the powers to detect evil, detect magic, and see invisible. It can also read magic and has the extraordinary powers extra damage, telepathy, and healing. It speaks Gnoll, Gnome, Goblin, Hobgoblin, Kobold, Ogre, Orc, and Pixie. Unsheathed, the sword raises the morale of all friendly troops within a mile of the wielder by 1.