In "The Whale Who Wanted to Sing at the Met", all of the operatic vocals - from the bass up through soprano, and even the chorus - were sung by Nelson Eddy. By tinkering with his home recording equipment (his father was a machinist), Eddy was able to sing and record sextets with himself for the soundtrack.
At the beginning of "The Whale who Wanted to Sing at the Met", Nelson Eddy sings a long sustained opera note. As he is singing it, animation is seen of newspapers blowing in the wind, lightning bolts flashing, and storm clouds forming. Also included in this brief animation sequence are a curtain blowing from the "Dance of the Hours" sequence in Fantasia (1940) and a witch or demon flying by on a broomstick that seems to have been taken from the "Night on Bald Mountain" sequence that was also in "Fantasia".
Willie seems to specifically be a sperm whale, a species that is the largest of the toothed whales and the largest toothed predator. The sperm whale's clicking vocalization, a form of echolocation and communication, may be as loud as 230 decibels underwater, making it the loudest sound produced by any animal.
Willie the Whale made minor appearances in House of Mouse - Il Topoclub (2001), including once paired with the similarly named Willie the Giant.