Today most Americans, including many Army officers, know very little about FAE weapons or their development, advantages, or dangers. Therefore, I first will briefly describe what FAE weapons are and how they work. Then I will recount some of my experiences with these new explosives, as well as warnings that I gave during the Vietnam War to prevent one type of FAE munition — those containing ethylene oxide, a combustible poisonous gas — from falling into the hands of the Viet Cong or North Vietnamese. Those weapons could have been used by our enemies to “prove” that the United States had initiated poison gas warfare. Also, I will describe some new, comparatively simple types of FAE weapons that can be developed for use by foot soldiers, and simple means to degrade the effectiveness of all types.
Dr. William G. McMillan of McMillan Science Associates, Inc. and Dr. Conrad V. Chester of Oak Ridge National Laboratory, both chemists, were the reviewers of drafts of this chapter who contributed most to its technical accuracy.
Fuel-air explosives are so named because they utilize the oxygen in the open air to oxidize extremely rapidly a combustible gas injected into and mixed with the air. (In contrast, the oxidizing agents in high explosives are solids constituting a large part of the explosives’ weight.) In an FAE weapon the combustible gas is contained in the liquid state inside a high-pressure cylinder until after the cylinder is ruptured by expertly designed linear shaped charges attached to its sides. Then the pressurized liquid rapidly disperses itself into the air, producing an expanding gas/air cloud.
When an FAE cylinder is ruptured several special detonators are simultaneously ejected, timed to go off after the dispersed liquid has become a gas and when the resulting gas/air cloud is a detonatable mixture. A detonation is a much more powerful type of explosion than a typical gas explosion, such as those I heard much about during my peacetime work in oil fields and mines. An ordinary explosion of a combustible gas, either in the open or in confined spaces such as mines or buildings, almost always is a deflagration — a very rapid burning of the gas/air mixture. A deflagration produces much lower blast pressures and much less damaging shock effects than does the detonation of the same gas/air mixture.
The most catastrophic gas/air deflagration in history was the natural gas explosion in June of 1989 that killed about 500 Russians out of over 1,200 on two passenger trains going through the Ural mountains. The trains went into an invisible cloud of an ignitable gas/air mixture covering several hundred acres. A mostly propane and butane mixture had escaped for hours from a broken 30-in.-diameter pipeline in the vicinity. Izvestiya, a prominent Soviet newspaper, described a mile-long “flame front” as having consumed the trains. To judge from pictures of the overturned, blackened cars, the twisted rails and displaced railroad ties, the “flame front” was a blast wave of a deflagration propagated from an ignition point some distance from the tracks. A fiery blast wave traveling only a few hundred miles per hour and striking the cars on their sides produced the dramatic impact effects on the cars and passengers, and burned many of the killed and the survivors.
Tragic as were the results of this huge deflagration, had the same gas/air cloud been detonated the catastrophe would have been much worse. The blast wave that would have swept against, through, and over the trains would have been traveling at a velocity of more than 1,000 miles per hour. Pressure of around 300 pounds per square inch would have instantaneously killed everyone inside the detonated gas/air cloud and the cars would have been hurled and torn apart.
FAE weapons can be made with non-poisonous combustible gases, including propane and other hydrocarbons, or with poisonous combustible gases. To broaden the range of hydrocarbon-air mixtures that can be detonated, small amounts of propyl nitrate can be added to the gas.
A variety of FAE ground-to-ground weapons can be developed that will be light enough for men on foot to carry to firing positions a few hundred meters or more away from valuable targets of types that can be destroyed much more effectively by FAE detonations than by the use of high explosive (HE) weapons of equal weight. FAE rockets designed to be carried by foot soldiers — as were the Soviet 122mm HE rockets with their quickly erected launching guides, used with deadly effectiveness in Vietnam — should not be overly difficult to perfect. Time will tell whether we or our enemies first develop and deploy such deadly new conventional weapons.
Several months before going to Vietnam in 1967 I began an unofficial experiment to detonate an ethylene oxide/air mixture, as described later in this chapter. Then I learned that both the Air Force and the Navy were far along on secret FAE weapon developments. To find if I might be helpful in contributing to improving FAE weapons I went to the Naval Weapons Center, China Lake, California. There civilians doing the experimental work informed me that development had been greatly complicated by the requirement to perfect an FAE weapon deliverable by a low-flying jet, rather than first making simpler types deliverable by helicopter or as mortar projectiles or rockets which would fall toward earth almost vertically and much more slowly. A second reason for slow progress was inadequate funding, largely due, I was told, to key generals’ lack of understanding of basic advantages of FAE weapons.
That was an FAE developmental difficulty which I thought I would be able to help lessen. One of the officers in charge of FAE funding was Lieutenant General Alfred Dodd Starbird, a West Pointer I had known at Princeton when he was a graduate student and we were taking some of the same engineering courses. I went to see him in Washington. Among the facts I gave General Starbird, explaining why FAE detonations are so lethal to men and so destructive to many blast-resistant targets, were the sizes of the areas that can be covered by blast pressures of at least 200 pounds per square inch at ground level, resulting from the detonation of stated weights of FAE weapons both on and at different heights above the ground. He said I was mistaken, that much smaller areas would be covered. He showed me a military engineering handbook that gave blast pressures at the outer edges of several sizes of circular areas, caused by different weights of explosives air burst near the ground at the centers of the different areas.
I explained that those listed areas and blast pressures were for HE explosions, with each weight of an explosive including the weight of its oxidizer, and each explosion being essentially a point source with resultant blast pressures of many thousands of pounds per square inch at and close to that point. A great deal of the energy of an HE air burst is wasted in accelerating material from the explosive and also accelerating the surrounding air before the blast wave reaches the outer edge of an area calculated to be subjected to at least a specified pressure. (A ground burst expends much additional energy rupturing and accelerating earth from its crater.) In contrast, the near-maximum blast pressure of about 300 pounds per square inch caused by an optimally exploded FAE weapon is produced throughout its properly dispersed and detonated cloud of combustible gas mixed with outdoor air. The outdoor air supplies the oxygen. The energy of a detonated FAE weapon is used much more efficiently against many military targets (ones which do not require extremely high blast pressures for their destruction) than is the energy of an HE munition. Inadequately sheltered people within a detonated FAE cloud are killed instantly.
A few months later I was told that the information I had given to General Starbird on FAE weapons had contributed to the continuation of their R&D funding.