We've seen this as an Orphan Annie premium from 1940. Ovaltine must have had excess supply because here is the same whistle and instruction folder but in a "Captain Midnight" mailer c. 1941-42. The whistle is NM and the most lustrous we have ever seen. It is 3-3/8" long and slides open to 5-1/8" long. The folder is 3-5/8x4.75" explaining numerous uses for the whistle and naming Ovaltine as the source for additional examples but mentioning neither Orphan Annie nor Captain Midnight. The thing that ties this into being a Captain Midnight premium is his specific return address on the mailer. Mailer has small crease marks as does the folder but both are in completely clean condition. From the Joe Gura Premium Collection.