The U.S. military is working “furiously” to rewrite its nuclear deterrence theory to deal with threats from China and Russia better.

Strategic Command chief Navy Adm. Chas Richard said the U.S. threats are “unprecedented in this nation’s history” during Thursday’s Space and Missile Defense Symposium in Huntsville, Alabama, adding, “We have never faced two peer nuclear-capable opponents at the same time, who have to be deterred differently,” according to Defense One.