Love the concept.

1. Make the protagonist a single character from which the point of view is established (In which case I would perhaps consider entirely omitting the other four navy men)
2. It could be about seeking revenge rather than simply robbing the antagonist, however, you should perhaps consider also the idea of turning the revenge positive rather than negative. For example, perhaps our protagonist seeks to expose to a military court of some form the corruption occurring in order to incur greater crackdowns on suspicious payments in order to prevent future deaths by wealthy lenders.
3. Perhaps there is a slew of suspects of the murder and the action is our protagonist attempting to navigate interweaving alibis and discovering who committed the murder and bringing them to justice.

Overall a solid concept, which just needs a little more development of spicing up the logline. Definitely contains exciting potential and I’d watch it.