Grand slam force Grand slam force The Grand Slam Force is a bidding convention in contract bridge that was developed by Ely Culbertson in 1936. It is intended to be used in cases where the combined hands of a partnership are so strong that a slam (winning at least 12 tricks) is a near-certainty and a grand slam (winning all 13 tricks) is a possibility. It allows one partner to gain information on the quality of trumps in the other partner's hand. When this convention is in force, a bid of 5NT (five notrump), when it does not conflict with other conventions used
History of contract bridge auction bridge made by Harold Stirling Vanderbilt and others. The most significant change was that only the tricks contracted for were counted below the line towards game and slam. That made bidding much more challenging and interesting. Another innovation was the concept of "vulnerability", a difference in the sizes of penalties incurred by partnerships that have or have not won one game. That discouraged sacrifice bidding to protect the lead in a rubber. Some other scores were adjusted to produce a more balanced game. Vanderbilt set out his rules in 1925, and within a few years contract bridge had so