"Are you still there?" was the first radio transmission received at Johnston Island hours after the TEAK thermonuclear test on August 1, 1958. The 3.8 megaton, 77-kilometer-high blast triggered an electromagnetic pulse (EMP) which stopped radio communications throughout that large area of the Pacific. The EMP was so severe that military and civilian aircraft had to be grounded in Hawaii. The TEAK fireball could be seen as far away as Oahu Island, approximately 525 nautical miles from Johnston Island. Eyewitnesses said the colorful display rivaled the "Southern Lights," also referred to as the Aurora Australis. Several scientists viewing the test had to duck into a shelter quickly because an error with the launch vehicle, a Redstone rocket, caused it to detonate directly over Johnston Island instead of 20 miles down range.

The US armed forces infrastructure, and American society at large, remain vulnerable to a debilitating attack by an electromagnetic pulse (EMP) generated by a high-altitude nuclear blast, a senior-level, congressionally appointed panel has warned.

Several potential adversaries, such as China, are capable of launching a crippling EMP strike against the US with a nuclear-tipped ballistic missile, and others, such as North Korea or even terrorist groups, could have the capability by 2015, the panel said in its findings that it unveiled to US legislators at a hearing on 22 July.

Panel members said this type of attack may be an appealing option, especially for an unsophisticated opponent. One possible scenario is a 'Scud' missile, with a modified nuclear warhead to maximise the EMP effect, launched from a barge off the US coast.

While the US military has grown increasingly dependent on computers, electronics and information systems, it has relaxed requirements for EMP-hardened systems since the end of the Cold War and its overall record of adherence to its guidelines for such robust equipment "has been spotty", they said. This trend continues "in the wrong direction", the panel noted.

Similarly, the US civilian critical infrastructure is not adequately prepared to deal with the effects of an EMP attack, according to the panel, which is known formally as the Commission to Assess the Threat to the United States from Electromagnetic Pulse Attack. Congress created the panel in 2000 out of concern that this issue was not receiving enough attention.

An EMP attack, for example, could place the nation's electrical grid "in danger of fundamental collapse", said commission chairman William Graham, who served as scientific advisor to US President Ronald Reagan in the 1980s. The overall effects could be long lasting and difficult to recover from, he added. An EMP strike would also be likely to knock out non-hardened satellites in low-Earth orbit "within days or weeks", he said, noting that commercial satellites are especially vulnerable. Interest in a big penetrating bomb is growing in some US defence circles, including the Defense Science Board (DSB), the senior policy advisory panel to the Secretary of Defense. It recommended in its February 2004 report on 'Future Strategic Strike Forces' that the Department of Defense "immediately undertake" a demonstration of a "bomber-delivered massive penetrator" weapon as part of a family of ultra-large bombs that would "improve conventional attack effectiveness against deep, expansive, underground tunnel facilities."

U.S. High Power Microwave Electromagnetic Bomb Pictured Below: