Chicago Crescent first took off after World War II, as veterans returning from Europe sought to adapt the game to American systems. (The New York game is somewhat earlier, but Boston's version also dates to this time period.)
For a long time the ruleset tended to deviate widely from standard MC sets; for example, a play of "Jarvis" gave an automatic doubling of LV for reasons having nothing to do with the station's intrinsic properties. However, the more recent rulesets have brought the game back to standard play.
With Loyola 2001 (L01) the HP2K ruleset was adapted to Chicago conditions, and play became very similar to London Underground play. The following ruleset, Library 2004 (L04), made a number of minor modifications to L01, mostly to reflect ongoing changes in the system. (L04 was actually ahead of its time by several months, as some of the changes were not complete when it was promulgated, but these discrepancies have been eliminated.) The major changes are
- Elimination of LV restrictions on the Douglas (54/Cermak) branch of the Blue line due to the work of the Douglas Renovation Project (still ongoing, but no longer affecting service).
- Elimination of the Yellow Line's vulnerability to wirecuts due to its conversion to third rail. (It should be noted, however, that the Metra Electric and South Shore lines retain this vulnerability-- though it is difficult to take advantage of it.)
- Inclusion of a foetal line, the Circle Line, plus a number of foetal stations: North/Elston, Chicago (Circle), Madison-United Center, Van Buren-Paulina, Blue Island, Wentworth-Chinatown, and North/Clybourn (Brown and Purple).
- Inclusion of a foetal Yellow Line Station: Old Orchard.