Pigeons and bats were both used in separate projects. You're thinking of the bat one.
Incendiaries were attached to bats, who were dropped from planes. And then expected to fly into buildings. Incendiaries go off. Building burns down.
Pigeons were used as the guidance system in an early smart bomb. Rather than tracking a target with a laser or GPS, trained pigeons would steer the bomb.
Never used in combat, but supposedly very, very effective. Strap time-delayed incendiary bombs to hibernating bats, put them in a bomb case, release them over Japan. The bats go hide in buildings and start 1000s of fires.
The project was canceled after one or more buildings on the base they were being trained burned down.