Commentary for Ketubot 18:23

He would write a bill of divorce for his wife- For if he died in war the bill would take effect retroactively from the day it was written-And it happened that Uriah [the Hittite] died in war.

For it is written-During the war of Shaul and your brothers etc. and David learned from his father Jesse to even lead [properly] like this when going out to war