Excalibur, a Diplomacy variant, was written and illustrated (map) by Kenneth Clark and published in War Bulletin (Issue 51 - Nov 1973), a "DipZine".
Excalibur relies on the normal 1971 rules for most aspects of play. Specific differences include an established order of precedence for retreat order (for units without a valid retreat order); off-board supply centers; relaxed unit build locations; and map-specific fleet movement rules ("sailing around Scotland").
Excalibur uses a custom map based on England, with sixty-two regions, nine on-board national supply centers, four off-board national supply centers, and twenty-three neutral supply centers. The national options include British, Picts, Scots, Saxons, Angles, Jutes, and Frisians. The Saxons, Angles, Jutes, and Frisians have special off-board unit starts and use differing initial placement rules. Play begins in Spring 450.
-User summary