Israel is widely believed to possess nuclear weapons as well as chemical and biological weapons of mass destruction. Israel has not signed the Treaty on the Non-Proliferation of Nuclear Weapons and maintains a policy of deliberate ambiguity toward its nuclear capabilities. The Israeli Navy's Dolphin submarines are believed to be armed with nuclear Popeye Turbo missiles, offering nuclear second strike capability. Since the Gulf War in 1991, when Israel was attacked by Iraqi Scud missiles, all homes in Israel are required to have a reinforced security room, Merkhav Mugan, impermeable to chemical and biological substances.