Project Golf was initiated by making a direct comparison between an imported 500-pound TNT-filled mediumcapacity bomb and an ANFO-filled 6mm steel casing having equal mass. Both units were mounted vertically on three-foot stands pointing nose down for command detonation from a safe distance. The imported bomb was detonated first. It went off with the usual bright flash, black smoke and a very loud bang with plenty of dust drifting away on the wind. The ANFO bomb was nothing like as impressive to the eye or ear. The explosive flash was nowhere near as bright as the TNT bomb and pasty-grey smoke mingled with dust was drifting off before a deep ‘crrrrump’ was followed immediately by a second ‘crrump’.
Inspection of the sites showed clearly that we had a winner in ANFO. Loud bangs, such as thunder from lightning, are the product of huge energy releases to atmosphere. In the case of bombs filled with high flame-rate explosives, bright flashes and loud bangs of surface bursts are products of wasted energy following the disintegration of steel casings. When used against buildings, bunkers and other targets where detonation occurs within confined structures, the same energy is highly destructive, but not so in the unconfined conditions of open bush.
In the case of ANFO, the steel containers swell in size, as do the high-explosive containers; but ANFO, having a much slower flame-rate, continues its heaving detonation well beyond case disintegration. An ANFO mix, when confined in a steel container and given a hefty thump by an initiator charge such as Pentolite, ignites spontaneously to generate enormous amounts of high-pressure gas in a heaving EXplosion which forces air outwards from the generated gas bubble. The gas cools immediately, creating a void into which the air flows at supersonic speed, causing an IMplosion.
Digressing for a moment, the implosion following an atomic bomb blast causes more damage to structure than the initial explosion. In the case of ANFO, explosion and implosion are equally damaging—a double dose of no good.
The production of ANFO, a commonly used mining explosive, simply involves the thorough mixing of a small quantity of diesel fuel into prilled ammonium nitrate fertiliser. In the beginning we did this with a shovel in a wheelbarrow. Later we progressed to a simple motor-driven concrete mixer for large-quantity production.
ANFO offered a special advantage. From the start we realised that it would not be necessary to use special ammunition dumps for the safe storage of ANFO bombs. Unlike standard high-explosive units that had to be filled in specialised conditions, ANFO bombs could be stacked in the open and only filled when they were needed.
Digressing again and returning to the Mao Tse Tung ‘ground cannon’ mentioned in conjunction with the CT ‘air ambush’ system, I decided to test this ‘cannon’ using ANFO as the explosive. A one-metre round hole was dug to a depth of one metre. At the base we placed a 20kg charge of ANFO then filled the hole with rocks.
The project team was over 1,000 metres away when the ‘ground cannon’ went off with a dull thunderclap. Whilst the rocks remained close together, their rapid passage up to around 1,000 feet above ground was obvious. Thereafter we could see nothing of individual rocks that soared on to greater heights. We watched the ground ahead for ages waiting for the rocks to land but neither saw nor heard anything. I was heading for my vehicle when a peculiar sound, which I can only describe as something like static electricity, developed all around. Everyone dived under vehicles in time to avoid the rocks that came crashing down.
Used in multiples around airfields, this crude device would have been devastating to enemy paratroopers and ground-attack fighters. Fortunately however, there was never a need to employ Mao Tse Tung’s crude but effective ‘ground cannon’.
Further static 500-pound ANFO trials were conducted before making a direct comparison between an imported 1000-pound bomb and an ANFO unit of equivalent mass. For this we acquired specially bred white guinea-pigs with black ears. They were placed in wire-mesh cages, set in deep holes (to protect them from shrapnel) next to which pressure pots and pressure discs were laid in a line at five-metre intervals from fifteen metres outwards to fifty metres from point of detonation.
The imported bomb explosion had no noticeable effect on the pressure pots and pressure discs beyond fifteen metres. In the fifteen minutes it took us to get to the test site, every guinea-pig, including the two at fifteen and twenty metres, had recovered from the big bang and were munching away at the feed in their cages.
Following detonation of the ANFO unit, we rushed back to the little creatures with a forensic pathologist in tow. I had persuaded this medical specialist to assist us in our ANFO tests by examining the bodies of snakes and frogs we found on the surface following every single ANFO detonation. All these cold-blooded creatures, though dead, appeared perfectly normal until dissected. Over-pressure had destroyed their lungs and other vital organs without any damage to outer skin. The frogs, which lived more than one foot below surface, were always found on top of the powdered earth, lying belly up.
At the 1000-pound ANFO detonation site we found every guinea-pig hunched up, motionless and covered in thick fine dust. Those at fifteen, twenty and twenty-five metres from blast had perished through overpressure. Those at thirty and thirty-five meters had perforated eardrums; the remainder recovered quickly enough but would not eat for more than ten hours. The pressure pots within twenty-five meters suffered distortion with permanent set and satisfactory over-pressure readings extended out to thirty-five metres.
The guinea-pigs that survived the ANFO blast were kept in a large pen separate from those that had been subjected to the imported bomb blast and Kutanga Mac looked after these little fellows better than any private home could. For reasons we never established, the guinea-pigs in the ANFO pen grew larger than the others and became enormously fat. The two deaf animals were the happiest, fattest and hungriest. All were eventually found good homes.
Our first ANFO bombs weighed 450kg, which was equivalent to the imported 1000-pound bombs. Canberras and Hunters released these in a series of tests. Although the tests themselves were successful, we were not at all happy with the loss of energy evidenced by large craters in the ground where they detonated.
Operational considerations clearly identified Hunters as the main user of high-pressure bombs, so we turned all attention to fighter/bomber style steep-dive (sixty-degree) profile attacks. To maximise blast effect each bomb was fitted with a one-metre-long proboscis to ensure airburst. To minimise energy losses downward and upward, and to maximise ground overpressure, simultaneous initiation of Pentolite booster charges at the front and rear of the ANFO charge resulted in a very satisfactory ‘squeeze’ effect. In doing this, each bomb flattened everything around the point of contact and no energy was lost to punching out ground craters. The entire tailpiece was usually found at the centre of detonation proving that almost no energy was going skyward.