Charles Ellicott Commentary 2 Samuel 11:15

"And he wrote in the letter, saying, Set ye Uriah in the forefront of the hottest battle, and retire ye from him, that he may be smitten, and die." — 2 Samuel 11:15 (ASV)

Retire ye from him. —This part of David’s orders was not carried out. Perhaps Joab thought it would make the stratagem too evident, or perhaps it was impracticable. In any case, the consequence was that others were slain with Uriah, and thus a larger bloodguilt fell upon David.