I don't want to hijack this thread even further than it already is but working with the British and Australian armies and their enlisted rank structure made me think about ours. Their corporals were much more mature and able than most of the Marine corporals that I have worked with; about on par with a Marine sergeant. Having a private-corporal-whatever structure makes more sense to me when E1-E3 in any service do the same job. Keep 'em at private until they earn corporal; 4 years of staring at the same rank may be an incentive...

On that note, 2nd LT and 1st LT are redundant as well.