13 Under their command was an army of 307,500 men trained for war, a powerful force to support the king against his enemies.

Read 2 Chronicles 26:13 Using Other Translations

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.
Under their command was an army of 307,500, who could make war with mighty power, to help the king against the enemy.
The army consisted of 307,500 men, all elite troops. They were prepared to assist the king against any enemy.