John Gill Commentary 2 Chronicles 26:13

"And under their hand was an army, three hundred thousand and seven thousand and five hundred, that made war with mighty power, to help the king against the enemy." — 2 Chronicles 26:13 (ASV)

And under their hand was an army, three hundred thousand and
seven thousand and five hundred
Which was larger than that in his father's time by 7500, (2 Chronicles 25:5) besides officers:

that made war with mighty power, to help the king against the enemy ;
they were ready to fight, and fight valiantly, whenever the king had any occasion for them, or the land was invaded.