1 Chronicles 12:33

went forth to battle, expert in war, with all instruments R.V. were able to go out in the host, that could set the battle in array, with all manner of instruments. This description is intended to exclude mere lads (such as David appeared to be, 1 Samuel 17:33) who might be in attendance on the warriors.

which could keep rank:they were not of double heart R.V. that could order the battle array and were not of double heart; i.e. who moved as one man in battle array; cp. 1 Chronicles 12:8, note on shield and buckler. For "of double heart" cp. 2 Chronicles 30:12, "one heart."