18 The passive participle of the verb “to choose” means that these were “choice” or superb chariots.
19 Heb “every chariot of Egypt.” After the mention of the best chariots, the meaning of this description is “all the other chariots.”
20 The word שָׁלִשִׁם (shalishim) means “officers” or some special kind of military personnel. At one time it was taken to mean a “three man chariot,” but the pictures of Egyptian chariots only show two in a chariot. It may mean officers near the king, “men of the third rank” (B. Jacob, Exodus, 394). So the chariots and the crew represented the elite. See the old view by A. E. Cowley that linked it to a Hittite word (“A Hittite Word in Hebrew,” 21 [1920]: 326), and the more recent work by P. C. Craigie connecting it to Egyptian “commander” (“An Egyptian Expression in the Song of the Sea: Exodus XV.4,” 20 [1970]: 85).

In other versions

and took six hundred chosen chariots and all the other chariots of Egypt with officers over all of them.

He took six hundred of the best chariots, along with all the other chariots of Egypt, with officers over all of them.

he took six hundred of the best chariots and all the rest of the chariots of Egypt, with officers in each one.

He took with him 600 of Egypt’s best chariots, along with the rest of the chariots of Egypt, each with its commander.

And he took six hundred select chariots and all the chariots of Egypt and officers over all of them.

And he took six hundred chosen chariots, and all the chariots of Egypt, and captains over every one of them.

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