<P> Progress cards are organized into three categories, corresponding to the three types of improvements . Yellow progress cards aid in commercial development, green progress cards aid in technological advancements, and blue progress cards allow for political moves . When a castle appears on the event die, progress cards of the corresponding type may be drawn depending on the value of the red die . Higher levels of city improvements increase the chance that progress cards will be drawn, with the highest level of city improvement allowing progress cards to be drawn regardless of the value on the red die . </P> <P> Progress cards, unlike the development cards they replace, can be played on the turn that they are drawn, and more than one progress card can be played per turn . However, they can generally only be played after the dice are rolled . Progress cards granting victory points are an exception, being played immediately (without regards to whose turn it is), while the Alchemist progress card, which allows a player to select the roll of the white and red dice, necessitates the card being played instead of rolling the numerical dice . (The event die is still rolled as normal .) </P> <P> Players are allowed to keep four progress cards (five in a five to six player game), and any additional ones must be discarded on the spot (unless the 5th card is a victory point, which is played immediately and the original progress cards remain). The only exception to this rule is if a player receives a 5th non-victory point progress card on his or her turn, in which case he or she has the option of playing any one of the five progress cards in his or her hand during the turn, thus bringing the progress card count back down to four . While this clarification is not overtly stated in the Cities & Knights rule book, it is enforced in the online version of the game . </P> <P> In total, there are 54 progress cards: 18 science, 18 politics, and 18 trade . </P>

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