KABUL, Afghanistan – For former CIA director David Petraeus, it was a one-year stint as top U.S. commander in Afghanistan. His replacement is scheduled to leave next year after 18 months in the job.

And now the sex scandal that draws them together – Petraeus' career toppled and Marine Gen. John Allen's possibly on hold – also has placed greater attention to the quick turnover of American battlefield chiefs in the 11-year war.

Nearly two dozen generals have commanded troops from the United States and the NATO-led International Security Assistance Force, or ISAF, since the American invasion in late 2001 – with five U.S. generals running both commands in the past five years alone.