Susannah and James Smith are your ancestors. After James died, Susannah married Thomas Jones. Susannah then died and Thomas married Cassandra Smithton. After Thomas Jones died, Cassandra applied for a military pension based on Thomas’ military service.
That pension may still be helpful to your research on Susannah. Cassandra would have had to mention all of Thomas’ marriages–including the one to your ancestor. There may be a detail in Cassandra’s application directly related to your ancestors or clues to help you in your research.