The Adventures of Young Indiana Jones: The Phantom Train of Doom (1999)

In the tenth film in the series, in November 1916, Indiana Jones and Remy Baudouin have managed to get a transfer from the European trenches to the plains of Africa. On arrival they both receive a promotion to the rank of lieutenant in the Belgian Army. When they take the wrong train they end up in Moshi. Desperate to join their unit in Lake Victoria, the two men bump into the 25th Royal Fusiliers, a unit of cranky old men led by Indy's old acquaintance Frederick Selous. Indy's passing knowledge of trains and fluent German comes in handy for the Fusiliers, who are about to go on a mission to find and destroy a Phantom Train that carries an enormous German artillery gun.

Unfortunately the movie The Adventures of Young Indiana Jones: The Phantom Train of Doom is not yet available on HBO Max.