You're right, the "t" is silent in the word "depot". The answer to why is that English spelling and pronunciation make exceptionally little sense^^ And English also draws from a lot of other languages. "depot" comes from French, where the "t" is silent. Some other words originating from French like this are: ballet buffet chalet crochet gourmet valet debut

We stole that word from French (along with many others), so we followed their pronunciation and kept the spelling.

You heard correctly. I found this site with more examples: http://evaeaston.com/sl-pat-td.html

Bouquet, Croquet, Escargot, Tarot, Denouement, Beret, Fillet, Chalet, Gourmet, Merlot, Cabaret, Cachet, Sobriquet, Rapport, Rapprochement, Ricochet. Here's a game :) http://www.jetpunk.com/user-quizzes/25596/vocabulary-words-ending-in-silent-t Also, https://pronunciationstudio.com/silent-t/