Now it fell on a day, that Jonathan the son of Saul said to the young man who bore his armor, Come, and let us go over to the Philistines' garrison, that is on yonder side. But he didn't tell his father.
As noted above, Saul's wars were very slightly recorded, but there is an exception in the victory against the Philistines revealed in this chapter.  Why?  The answer lies in the shameful and sinful behavior of Saul which prevented the victory from being complete and which led to a perpetual war with the Philistines all of Saul's life, ending finally in his death on Mount Gilboa.