Bergen Two-Under Transfer Preempts

Preemptive openings of 3

and higher can be used to show the suit two steps higher than the one bid. For example:

x QJTxxxx xx xxx

x KQTxxxx Kxxx x

These are possible 3 bids, but are substantially different in playing strength. If 3 is bid with both hands, the responder may have to guess. Bidding 3 to show a 3 opening allows the responder to bid 3 if he wishes to invite 4. This has the usual advantage of transfer bids, in that partner becomes the declarer and the lead comes up to his possible tenace position. A disadvantage is that it places less pressure on the opponents in the bidding: Second hand will have two opportunities to act.

From The Official Encyclopedia of Bridge, Fifth edition