An Unusual Gambit
If White wishes to play the "Bird-Larsen" opening, he most often avoids the very direct 1.f4 d5 2.b3 move order. That is because Black has a chance to cut across this scheme with an early ...d5-d4, as in the game below. If the first player delays b2-b3 in favor of Kingside development, then Black can fianchetto with ...g7-g6 himself to hinder White's plan. In any case, those who play Bird's Opening have found ways to maneuver around this ...d5-d4 thrust, but an aggressive gambit alternative would be welcome too!
The following game was played in section 87NF11 of the 1987 US Correspondence Championship. White tested a little studied gambit which can be made a surprise weapon even today. The gambit arises after 1.f4 d5 2.b3 Nf6 3.e3 d4 4.Nf3 dxe3 5.Bc4 (or 5.Bb2), aiming to speed development and open central lines of attack. There follows 5...exd2+ 6.Nbxd2 and after 7.Bb2 next White will then place his Queen on e2 and castle Queenside with a very energetic position.
In those days computers weren't around, so now it should be easier to form a judgment about this gambit. In practical time-controlled tournament play White's pawn sacrifice is certainly playable, and offers active chances. This variation can be classed as a "positional" gambit, an opening pawn sacrifice for tempo and long term pressure - in spirit akin to the Smith-Morra gambit. However, this system awaits trials in high level computer analysis, and few top chess players seem willing to test the 1.f4 d5 2.b3 move order. All in all, a fertile field for investigation!