Nuclear triad
Israel is known to have nuclear-capable aircraft and land-base missiles, with the addition of nuclear-armed submarines this would mean that they now have a full triad of land-, air-, and sea-based nuclear delivery systems some of which would be invulnerable to a first strike by an enemy for the first time in their country's history. No other nation in the Middle East in known to be in possession of nuclear weapons, even though Iran, Iraq, Syria and Libya have started development programs that were never completed.
High-alert nuclear weapon
Virtually all "high-alert nuclear weapons" are possessed by the U.S. and Russia. Both nations use automated command and control systems in conjunction with their early warning radar and/or satellites to facilitate the rapid launch of their land-based intercontinental ballistic missiles (ICBMs) and some submarine-launched ballistic missiles (SLBMs). Fear of a "disarming" nuclear first-strike that would destroy their command and control systems and nuclear forces led both nations to develop "launch-on-warning" capability, which requires high-alert nuclear weapons able to launch on a 30-minute (or less) tactical warning, the nominal flight time of ICBMs traveling between the U.S. and Russia.