Friday, November 18, 2011

Operation Outward

Isn't it amazing how you find fascinating stories buried in the folds of history, stuff you never realized was there? Well, I came across such a story recently and I wanted to share it with you, my seven readers.

As an electrical engineer, I really enjoyed reading this story. We always hear about how terrorists can attack us by bringing down our power grid, and this is a legitimate worry. Well, in World War II Britain used a simple plan to try to attack Germany this way--and I had never heard of it until now! From IEEE Power & Energy magazine:

"Operation Outward, Britain’s World War II offensive balloons" by Raoul E. Drapeau
http://sites.ieee.org/ny-monitor/files/2011/09/OPERATION-OUTWARD.pdf

Britain launched balloons, with trailing cables, towards German power lines. Lots of details to make it work, but a very simple concept. In August 1942, according to the article, they were launching 1000 balloons per day! Who knew?

"Operation Outward was a British Admiralty program that, between March 1942 and September 1944, manufactured and launched almost 46,000 inexpensive hydrogen-filled meteorological balloons trailing a length of wire intended to contact and short circuit overhead high-voltage and lower-voltage transmission and distribution lines in Germany and in occupied Europe. By all accounts, this campaign succeeded in randomly disrupting target electrical systems, was conducted with relative safety to Women’s Royal Naval Service (WRNS) personnel involved, and was extremely cost effective. In addition to the actual damage caused and the loss of electric power, Operation Outlook had significant harassment value by imposing extra demands on German air defenses and aviation fuel supplies."

First the article gives some background:
"Surprisingly, the trials showed that even a thin steel wire (much thinner than that used to tether the static barrage balloons), when drawn in sliding contact across two or more phases, could cause an arc as long as 15 ft (4.6 m) that would be maintained until the circuit breaker opened. In some cases, the arc’s heat melted the aluminum outer layers and then the reinforcing steel center strands of the conductors. Further, even if not severed, the conductors would be so weakened by the arc that they would be susceptible to breaking due to increased load demands or even normal weather events such as wind, snow and ice. Then, even if the trailing wire was severed by the arc, the balloon with the remaining portion of the wire could be carried along with the wind to engage yet another electric line."

Brilliant! I love the engineering discussion in the article, too.

"The British knew that the German high-voltage electric transmission system was protected by Petersen coils, which could not cope with phase-to-phase shorts of the type that would likely be caused by the balloons’ trailing wire. Further, they knew that the German systems of that time used slower-acting circuit breakers, also not designed to handle phase-to-phase shorts. The British concluded that this design could lead to the destruction of the circuit breakers and transformers and cause even more catastrophic faults, such as wrecking an entire power generating station, which actually happened in 1942."

"Even though the British electrical system had a more developed grid than that of Germany, which could make it more vulnerable, it also had faster-acting circuit breakers, and had proven itself more capable of tolerating (but not be completely protected from) hits from errant barrage balloon cables. This made the British less worried about the effects of possible retaliation and more encouraged about the potential of trailing wires as a weapon."

"Further supporting the argument that trailing wires could be an effective weapon was the idea that since the balloons would be released in large numbers, they would be likely to cause numerous faults in the same area, thereby complicating the task of repair and further diverting valuable resources. Also, even a single balloon could cause multiple disruption events as its long wire dragged along the ground."

"Considering the shortages of materials for repair of electric power systems in England and especially in Germany, it was clear that the consequential damage of a balloon strike could be much greater than that caused by a single bomb dropped from an aircraft."

So, was the campaign effective?

"One of the most important instances of damage was the 12 July 1942 complete destruction of a power plant at Böhlen near Leipzig due to an Outward balloon that had been launched on 11 July 1942. A phase-to-phase short on a 110-kV overhead transmission line caused the circuit breakers to malfunction, causing one of the 16.5-MW generators to be thrown out of synchronism and begin to vibrate. Its rotor shaft bent, causing mechanical interference withthe fixed stator, followed by an explosion and a fi e that destroyed the power station. This event put 250 MW of generating capacity out of operation for an extended period. The value of that material loss was estimated by the team at £1,000,000 (US$4,250,000) in 1942 currency, not including the value of production time lost."

"The assessment team learned that the Germans realized the potential damage of the balloons and gave orders to shut down power lines in their path and make the circuit breakers more sensitive. However, the latter change made the system more sensitive to normal occurrences such as bird strikes and overloads and exacerbated the power outage problem. There were far more incidents on the more common lower-voltage lines, some of which would suffer from multiple failures. Worse, even though the breakers might have been reset and power restored, the lines often suffered damage to the wires that would become apparent later under heavy loads or adverse weather, when they would break."

"The team retrieved a report that showed that in the period from March 1942 through the end of January 1943, there were 520 major disturbances on German high-voltage lines of 110 kV and higher. In that same period, there had been about 25,000 Outward balloons launched. Belgian, Dutch, and French transmission lines also suffered. In France alone, over the entire program, there were 4,946 recorded incidents of power interruptions. The postwar assessment reports were quite specific in most cases about Operation Outward balloons being the cause of the damage cited."

"The team’s conclusion was '. . .the evidence obtained shows that these Outward attacks were a continual menace to the whole German Electric Supply system for even minor incidents caused continual interruptions to the power supplies with damage to the equipment involving diversion of manpower on repair work, to say nothing of production delays. The destruction of Böhlen alone however was an ample reward for these operations.' In another communication, the team wrote 'the result of the operation was out of all proportion to the man-power and material employed.' In fact, in some months, there was more damage done to electrical systems by the balloons than there had been by bombers—and at a much lower cost to Britain."

What a great story. Engineers kicking ass, I love it!