Six hundred chosen chariots - The Egyptian army comprised large numbers of chariots, each drawn by two horses, with two men, one bearing the shield and driving, the other fully armed. The horses were thoroughbred, renowned for strength and spirit. Chariots are first represented on the monuments of the 18th dynasty. By “all the chariots of Egypt” we are to understand all that were stationed in Lower Egypt, most of them probably at Rameses and other frontier garrisons near the headquarters of Pharaoh.
Captains - The word שׁלישׁ shâlı̂ysh, literally “third or thirtieth,” may represent an Egyptian title. The king had about him a council of thirty, each of whom bore a title, Mapu, a “thirty man.” The word occurs frequently in the Books of Kings. David seems to have organized the Shalishim as a distinct corps (see 2 Samuel 23:8 Hebrew), retaining the old name, and adopting the Egyptian system.