The B-36 was the first intercontinental bomber able to carry any weapon in the U.S. arsenal across distances up to 3,900 miles. Thus, it was the principal means of deterrence from 1948 to the late 1950s. It was flown extensively in later atomic weapons tests at the Marshall Islands and at the Nevada Proving Ground. Yet, in its entire history, the "Peacemaker" never dropped a bomb in combat. Although the six-engine B-36 bomber was one of the newest aircraft in the USAF, it was not initially designed to carry atomic weapons and therefore required modifications in order to be coupled with such weapons. These modifications and weapons marriage occurred at Kirtland under the HQ Squadron 3170th Special Weapons Group.