I'm thinking a 1928 Trojan.
The case is marked "Bulova" and "American Standard" with a June 10, 1924 patent date. Its 14K gold filled. The moment is a 15J 10AP marked 1927. 15J is constant with other Trojans but this would be the first Trojan with a 10AP movement. I see these 10APs scattered in the database associated with various models from the 1920s that appear to usually have 10AN movements. So I think its original.
This thing runs. Its definitely showing its age but I got a good deal on it.