Thach weave (or formally known as 'Beam defense position') is an aerial combat tactic developed by naval aviator John S. Thach of the United States Navy soon after the United States' entry into World War II
Thach weave was executed either by two fighter aircraft side-by-side (as illustrated) or by two pairs of fighters flying together. When an enemy aircraft chose one fighter as his target (the "bait" fighter; his wingman being the "hook"), the two wingmen turned in towards each other, bringing the enemy plane into the hook's sights. A correctly-executed Thach Weave (assuming the bait was taken and followed) left little chance of escape to even the most maneuverable opponent.
The maneuver was so effective that it was used by American pilots during the Vietnam War, and is still an applicable tactic today.