This is a rare sound effect (likely created by MGM) that was used mostly in the MGM cartoons from 1938-1946. It debuted in the Captain And The Kids cartoon "The Winning Ticket". It may be a prototype of the Famous Studios Cartoon Fall Sound, although it shouldn't be confused with the Warner Bros./Famous Studios variants of that sound effect.
Barney Bear (Heard in "The Flying Bear" and "The Uninvited Pest".)
MGM Cartoons (Heard once in "The Winning Ticket", maybe "Peace on Earth" (heard with Sound Ideas, WHINE, CARTOON - SHELL SCREAMING WHINE DOWN), "Red Hot Riding Hood" and "What's Buzzin', Buzzard?"; twice in "The Stork's Holiday" and "The Lonesome Stranger", and multiple times in "The War Dogs" and "Blitz Wolf".)
Tom and Jerry (Used once in "The Bowling Alley Cat" [1st half, reverse and normal edits], "Yankee Doodle Mouse" [1st half], "The Mouse Comes to Dinner" [briefly], "Tee for Two", and "Springtime for Tom" [long form].)
You, John Jones (1943) (Heard partially when the bombs drop)
Trailers
Bataan (1943) (Trailers)
Image Gallery
Barney Bear MGM BOMB, WHISTLE - LONG BOMB FALLING WHISTLE in "Barney Bear and the Uninvited Pest"