Saturday, May 24, 2014

A blast from the past - a low-tech cluster bomb

My current novel concerns a war between two minor, insignificant planets in an era of interstellar travel.  Because both are minor polities, they don't have access to and/or can't afford all the most hi-tech weaponry deployed by major powers;  so many elements of their armed forces, tactics and strategy are more reminiscent of earlier eras.  It's a lot of fun trying to blend the two scenarios into a seamless whole.  I hope you'll like it when it's finished.

As part of the process, I describe in great detail a final, climactic engagement between the two sides, including the use of cluster bombs.  I drew on my knowledge of one low-tech (but very effective) cluster bomb design to describe one of the weapons involved;  but an alpha reviewer was taken aback by my outline.  He protested that cluster bombs were far 'higher-tech' than that, and claimed something such as I described would never work.

However, what I describe in my novel is an actual weapon that was designed in the 1970's, further developed in the 1980's, and did significant damage to its targets in both decades.  It began life as the 'Alpha bomb' in what was then Rhodesia.  Its design was inspired by Peter Petter-Bowyer, a career officer in the Rhodesian Air Force who helped produce a great many of that small but ferociously effective air arm's indigenous weapons.  The Alpha bomblet was designed to be dropped from 'hoppers' in the bomb bays of Canberra strike aircraft.  Petter-Bowyer emigrated to South Africa after Rhodesia collapsed, and helped that country's engineers to further develop the Alpha bomblet design. It was incorporated into the CB470 cluster bomb, which packed 40 Alpha bomblets into a conventionally-shaped bomb casing, allowing them to be dropped from pylons beneath the wings and fuselages of aircraft without bomb bays.

Here's Group Captain (i.e. Colonel) Petter-Bowyer's description of how the Alpha bomb was developed in the mid-1970's. It's taken from Chapter 8 of his autobiography 'Winds Of Destruction', which is relatively long, but worthwhile reading for military and aviation history buffs.  (The illustrations below are from various sources, but after the passage of so much time across several continents I've no idea who originated them or who owns the copyright - I've found them in several locations.)

... for accuracy to be assured, the Canberras would have to pass over target in perfect range of missiles and guns. The alternative was to bomb from great height and accept both loss of accuracy and the fact that cloud could limit windows of opportunity for strikes. Neither of these situations was acceptable. Another unacceptable issue, no matter the bombing height, was that large gaps in a string of bombs left too much ground uncovered.

An inherent problem with conventional bomb design is the need for tail cones and stabiliser fins that are costly and occupy potentially useful space in a bomb bay. Spherical bombs are quite different. They do not poses wasteful appendages, nor do they suffer orientation problems. A spherical bomb bursting above ground will consistently deliver shrapnel through 360 degrees in all directions but always lose half into the air.

Delivered in clusters, spherical bomblets moving through air at high speed create high-turbulence wakes that induces lateral movement to following bomblets. Moreover, high drag on every bomblet causes rapid deceleration from the moment of release. Another important advantage is the natural tendency of round bombs striking the ground at shallow angles to skip back into flight, making airburst possible. Admiral Nelson used this principle to good effect against enemy ships by skipping round cannon shell off water to improve the chance of gaining waterline damage.

Having understood these explanations, Denzil and Bev were eager to assist us develop a spherical cluster-bomb system for Canberras because it was agreed that such a system was within the technical competence and capacity of the company. Denzil kindly undertook the initial research work at his company's expense and I opened a project file marked `Project Alpha'. Projects that followed were Projects Bravo, Charlie, Delta, etc.

Bev considered it necessary to use a central spherical bomb-core fashioned from 8mm steel plate to house the explosive charge and a multi-directional delay-fuse. This fuse would initiate a pyrotechnic delay-train, without regard to the orientation of a bomblet when it struck ground. The central core was to be encased within a larger 3mm steel sphere with many super-rubber balls tightly packed between the inner and outer casing.

The purpose of super-rubber balls was to allow the inner core to compress them on impact with ground thereby creating a latent energy source that would enhance a round bomblet's natural tendency to bounce into flight. At the time we did not see that the rubber interface would be giving bomblets vitally important secondary characteristics. One was an inherent ability to absorb sharp shock loads on the fuse if a bomblet was inadvertently dropped onto concrete during handling & loading.

A variety of tests were conducted to prove prototype bomblets' ability to recover off ground even when dropped vertically from a helicopter at great height. When we were certain we had a worthwhile project on our hands, I went to the Air Force Commander's office late one afternoon with an 8-inch bomblet in my hands.

Having explained the design, I held the ball at waist height and asked Air Marshal McLaren to watch how the bomb recovered into the air after impacting the ground, whereupon I released the ball onto his office carpet. His reaction to the metallic clang was not what I expected and I do not think he even noticed the bounce. "Get that confounded object out of this office. You have six weeks in which to produce your system for full load strikes by four Canberras." I was astounded by such a quick decision and said, "Sir, there is no money budgeted to meet your instruction!"

Mick McLaren was known for his ability to come to quick decisions. His reply was typical. "You concern yourself with technical matters and I will take care of the money. I am counting on you for success. You have six weeks to do the job, so get cracking!"

. . .

I made a telephone call to Denzil and told him we had `green light' on the Alpha Project and that Ron and I would be around to see him immediately. Denzil and Bev were waiting for us in the Company Boardroom together with the company's accountant and a third engineer. Our excitement was somewhat tempered by the realisation that a project of this nature, if undertaken in the USA, would require many millions of dollars, involve many engineers and would take no less than five years to complete.

With only six weeks to finalise research and development and produce four complete carriage and release systems along with hundreds of bomblets, it was obvious we had to make final but correct decisions right away. Denzil did some preliminary calculations that made it clear that cutting of metal had to start next day. In turn this meant we had to finalise the specific dimensions of both inner and outer casings at this very meeting so that preparation for half-sphere presses could be initiated that night.

Canberra bomb-bay drawings were spread out on the Boardroom table to confirm preliminary designs generated during our earlier work. I had to specify the number of bomblets in a single load so that Denzil and Bev could calculate final bomblet dimensions. For convenience we had already started referring to the bomblets as Alpha Bombs (Project Alpha) and I gave the operational requirement as 400 Alpha bombs to be released from eight independent containers, which we named 'hoppers'.

The engineers quickly sketched profiles of four units comprising two hoppers each to establish the internal volume of each hopper. Having done this, they established that the external diameter of each Alpha bomb would be 155mm. From this the size of the rubber balls and inner bomb core were also determined.

The very next day preparations were in hand to press the metal blanks into half spheres. By Day Three the welding of half-spheres for inner cores and outer casings was already under way. The first hundred outer casings were taken off-line and filled with concrete for initial proving trials.

At New Sarum Warrant Officer John Cubbitt had his Drawing Office staff busy finalising the hoppers design and within two days Station Workshops were fabricating prototypes for preliminary drop trials of the concrete-filled Alpha bomblets. The concrete units approximated very closely to the calculated final weight of explosive ones.

. . .

First drop tests of the Alpha bombs were recorded ... and we were delighted to see how cleanly they dropped away and how rapidly they spread out and trailed back from the aircraft. Because the concrete Alphas suffered little damage on impact, we were able to gather them up for repeat drop trials, including releases at low-level. All low level runs were filmed from the bomb bay, by a chase Vampire and from the ground. The results were very encouraging. Impact with the ground was occurring well behind the aircraft, lateral spread was better than expected and every unit skipped back into flight.

By the seventh week, one week behind schedule, the engineers were totally exhausted from their intense work schedule and many sleepless nights. However, we were ready to demonstrate to the Air Staff a full-scale Alpha strike on a 1,200 by 200-metre target that had been prepared by the Range Warden, `Kutanga Mac'. Hundreds of cardboard and steel targets were set above ground and in trenches throughout the length and breadth of the target.

. . .

There was great anticipation and mounting excitement as Squadron Leader Randy du Rand opened his bomb doors late on his run-in at 400 feet at a speed of 300 kts. None of the Air Staff expected such a spectacle of dust and multiple airburst flashes as 300 bomblets did their thing. That the Alphas were bursting at perfect height well behind the Canberra was obvious to all before the sound of the explosions reached the observation point. This came as a thrilling continuous thundering of overlapping explosions.

The Commander was quite overcome by what he witnessed and showed it by shouting, "Bloody marvellous. Absolutely bloody marvellous!" Everyone present congratulated everyone else before we all set off to walk the full length of the prepared target area.

First inspection made it clear that the Alpha Bomb system was just what we needed. When the visitors left, the project team commenced the detailed study that showed that the effective coverage of 300 Alphas was 1,100 metres in length by 120 metres in width.

. . .

The important thing was that the Alpha system was cleared for operations and the Canberra had been given the anti-personnel punch it deserved.

There's much more in his book.  I highly recommend it.

South Africa further developed the Alpha bomblet and incorporated 40 of them into the CB470 cluster bomb, illustrated below.

This was dropped by Mirage fighters of the South African Air Force against terrorist targets in Angola and (reportedly) Mozambique during the mid-1980's.  It was also sold to Iraq, which deployed it against Iranian forces during the Iran-Iraq War.  Iraq reportedly reverse-engineered the Alpha bomblet and produced at least some of its own version.  It claimed to have destroyed its stocks after the first Gulf War, but after the second Gulf War US forces found stocks of Alpha bomblets in Iraq on at least one occasion.  (They didn't initially recognize them for what they were, since the weapon was not widely known outside Southern Africa.)

The Alpha bomblet and CB470 cluster bomb have now been withdrawn from service in South Africa, and as far as I'm aware are not in use anywhere else in the world.

It was a remarkable achievement by Rhodesia in the 1970's to develop so effective a weapon at such low cost.  A typical Western cluster bomb costs tens or even hundreds of thousands of dollars, depending on the number and sophistication of its bomblets.  The Alpha bomblet cost less than $10 apiece to produce at 1970's exchange rates, and a decade later a full CB470 cluster bomb could be manufactured for well below $5,000.  They were not only operationally effective, but highly cost-effective as well.

Also very effective was the South African 'ball-bearing bomb', which was described by Flight International in 1986 as follows.

The 120kg [264-pound] low-drag shrapnel bomb is filled with 27kg of RDX/TNT high explosive surrounded by steel balls cast in epoxy between the outer glassfibre skin and the explosive core.  The carrying envelope of the weapon is up to 600kt/M0.95 at up to 40,000ft.

. . .

Nose impact fuzing is fitted, which can be either instantaneous or with a delay element of between 2-18sec;  a tail fuze is provided as a backup.  Alternatively the weapon can be fitted with a proximity nose fuze set for air burst.

. . .

The number of steel balls per bomb vary as to size, with 42,000 6.7mm [17/64" or 0.263"] balls, 26,000 7.9mm [5/16" or 0.311"] balls, 19,500 8.7mm [11/32" or 0.342"] balls, or 15,000 9.5mm [3/8" or 0.374"] balls.

There's more at the link.

I was given to understand during the 1980's, when I was working on other weapons-related projects in South Africa, that the ball-bearing bomb was developed for a specific mission.  Apparently a large-scale parade of terrorists was being planned in a neighboring nation to welcome a particular VIP.  It included a fly-past of four fighter aircraft.  South Africa learned of the plan several months ahead of schedule.  A proposal was made to intercept the 'enemy' fighters with South African planes and shoot them down, while four more South African strike aircraft would mount a flypast in their place - each carrying eight ball-bearing bombs. With careful formation planning, it was believed that the entire area of the parade ground could be pulverized, blasting every square yard of space with up to half a dozen ball-bearings.  That would in theory have been sufficient to kill or severely injure everyone on parade.

As far as I know the plan was never put into operation, but it inspired a very nasty weapon indeed, one that apparently served in other operations to good effect.  The larger, heavier ball-bearings proved more useful in thick, heavy bush, as they could penetrate it more easily with their greater momentum.  With the smaller ball bearings, a pattern of these bombs accurately dropped by a Mirage strike aircraft could clear an area almost as large as a football field of almost all living things.

(I might add that the Alpha bomblets were the cause of considerable heartburn to the 'brass' in the operational area at one time.  You see, soldiers get bored.  When they get bored, they look for distractions.  One such distraction, at a base that shall remain nameless, was to build a trebuchet out of scrap steel, 'borrowing' the maintenance section's welding equipment for the purpose.  The result was a most impressive machine that could hurl small rocks to a considerable distance.  Over a few beers one night, one of its constructors came up with a bright idea.  If it could hurl stones, why not try to hurl Alpha bomblets?  A co-operative Air Force sergeant was unearthed, who carefully emptied a CB470 unit of its bomblets and handed them over in exchange for a couple of cases of beer.  For several nights thereafter the miscreants would lob one, or two, or three Alpha bomblets at a time into the bush beyond the wire and guard towers, producing alarums and excursions among the guards on duty at the time and the expenditure of considerable vexation by the Powers That Be.  When the truth was discovered . . . let's just say that various and sundry punishments were threatened, including the permanent loss of canteen [PX] privileges for all concerned.  However, since they were on the point of rotating back to South Africa anyway, they didn't lose too much sleep about it!  No word on whether anyone ever found out which Air Force sergeant was involved.)

There's your bit of esoteric weapons history for the weekend.



Ed Stoutenburg said...

Hello-Sounds like an interesting scenario with different Tech Levels.David Drakes Sci Fi series on 'Falkenberg's Legion' by-baen paperbacks i think-was always a favorite to read when i was in the Service.Also the SciFi RPG game 'Traveller',by Marc Miller-wich is still going strong after 30 odd years-has a Lot of good modules with mixed Tech weapons.You can find many Fan pages on line ane reprints of original game module books.I'M sure there are Many more in print/online that i'm not familiar with-[Check out 'RPG Online also]

Anonymous said...

Sort of somewhat related (low-tech bomb) is the "concrete bomb" I read about during the Iraq war.
Seems the British developed a kinetic energy bomb that was basically a big steel tube filled with concrete.
The thinking is that a 1000 pound weight, hitting your house at about 600 miles per hour, will pretty much ruin your day without blowing up the houses around you.