The Pentagon's top lawyer has resigned and says he will return to private practice.

Jeh (jay) Johnson is stepping down at the end of December after four years that included a number of controversial legal issues including the escalation in the use of drone strikes, the revamping of the use of military commissions rather than civilian trials for terrorism war-era detainees, and the repeal of the Pentagon's ban on openly gay military service.

Johnson left the New York City-based law firm of Paul, Weiss, Rifkind, Wharton & Garrison, LLP, to take the Pentagon job, and is expected to return there.

In recent remarks in London, Johnson defended the use of lethal drone strikes, saying the U.S. relies on the law of war and on the principles of proportionality and necessity.