• NAME: Harlo "Terry" Taerum
  • BORN:  May 22, 1920 (Milo, MB)
  • DECEASED:  September 16, 1943 (Dortmund-Ems Canal, Germany)
  • EPIC BATTLE:  Operation Chastise
  • RANK:  Flying Officer
  • HONOURS:  Distinguished Flying Cross

Our Intention is to educate Canadian Citizens so that they:

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  • Understand the role our military history has had in shaping our country and the world.
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May 22 1920 - September 16, 1943

For the extended version of the above video, please click here.

May, 1943: Fortress Europe appeared as invincible as ever. The Atlantic Wall stood strong, and the fiasco of the previous year’s Dieppe raid only reinforced this perception. Although the aerial Battle of Britain had been won, the Kriegsmarine’s u-boats continued to wreak havoc in the Atlantic, ensuring that the British Isles would remain under constant threat of starvation.  There were few means available to strike back at the Nazis and morale was low – strategic bombing was too broad an action around which to rally the people. Something specific was needed. Something daring. Something which will live on in popular memory for decades to come, inspiring dozens of movies and books. That something, as it turned out, would be made possible by one Calgarian: Harlo “Terry” Taerum.

But first, the event itself.

The Mission and the Challenge

Flying in specially-modified Avro Lancaster heavy bombers, the nineteen aircraft of 617 “Dambuster” Squadron, led by 24-year-old Wing Commander Guy Gibson, were responsible for destroying three primary hydroelectric dams in the Ruhr Valley: Möhne, Eder, and Sorpe. If the mission was successful, the dams’ destruction was expected to significantly setback Germany’s industrial output by depriving factories of both the electricity generated by the dams and the fresh water held in the reservoirs, not to mention the physical damage caused by the sudden ensuing flood.

The Möhne Dam before the Raid. Image courtesy of UK National Archives.

Accomplishing this mission would be no easy task, however. A dam’s utility is only eliminated when it ceases to hold back enough water to create the water pressure necessary to turn the turbines that generate electricity. This means creating a breach in the dam that extends all the way to the bottom of the structure to ensure that no water remains in the reservoir. In order to do this by aerial means, any ordnance had to be essentially adjacent to the bottom of the dam when it explodes.

Simple in theory, but difficult in practice - especially when the enemy is prepared for it. The logical solution to a problem that involves underwater demolition via aerial means would be an air-dropped torpedo: simply fly in the general direction of the dam and release the weapon. However, the Germans were well-aware of this possibility, and had set up a series of anti-torpedo nets in the reservoirs. The only way to get past the problem of the nets would be to drop the explosive between the last net and the dam structure, a deed requiring either the accuracy of guided weapons (not yet introduced) or extremely low flying right next to the dam structure, which would almost guarantee that the plane would not be able to pull up before it, too, slams into the dam.

So the tactical problem posed was thus: the bomber needed to be able to drop the weapon far enough away from the dam so it has time to pull up before reaching the dam, and the weapon needed to both reach and explode underwater at a significant depth between the last torpedo net and the dam structure.

A side-view of the solution (Fig. 14.). Image courtesy of UK National Archives.

The solution came in the form of a “bouncing bomb” (not to be confused with skip bombing), developed by British engineer Barnes Wallis. Essentially a 4,000kg spinning depth charge, the “Upkeep” device was used operationally only once: Operation Chastise. Chastise was the name of the “Dambusters” raid led by Wing Commander Guy Gibson on May 16-17, 1943, by 617 Squadron. Each of the squadron’s Lancaster bombers could only carry one Upkeep due to its weight and size. Upkeep worked by spinning backwards at 500 revolutions-per-minute (RPM). When dropped at very specific height, speed, and distance from the target, it was possible to make Upkeep reach that target by simply skipping multiple times over the surface of the water, thereby bypassing the underwater torpedo nets, and allowing the plane to drop Upkeep with enough distance to pull up.

A close-up view of the Upkeep device (or more likely a dummy test unit) in its carriage below the bomber. Photo courtesy of UK National Archives.

For Chastise, the required parameters were as follows: 18m above the water’s surface, speed 390km/h, and at a distance of 390m away from the dam. If any of these numbers were off, Upkeep would either lose energy long before reaching the dam wall or have too much “bounce” left and leap over the top of the dam. If done correctly, the bomb will have just enough energy to travel all the way to the dam and simply drop down the wall to the bottom of the reservoir before exploding at a preset depth of 9m like a conventional depth charge. The underwater explosion, as with a torpedo or depth charge, would cause damage not just by the initial burst, but also by the water rushing back into the vacuum created by the explosion – the inrushing water would punch into the dam’s wall, which is why it was so important that Upkeep had to have just enough energy to reach and roll down the dam wall. Flight instruments at the time were not precise enough to determine altitude as precise as 18m, so a pair of spotlights that were angled so they converged at 18m altitude was installed on all of the participating aircraft. As well, due to the lack of onboard radar, the only way to determine when the aircraft was 390m from the dam was to use a jury-rigged triangular instrument that would have both ends line up with the guard towers on either ends of the dam. The ingenuity of the engineers and airmen was impressive to say to least.

A Lancaster bomber modified for Upkeep employment. Note the removed upper turret to save weight and the addition of the mechanism under the bomb bay that would hold and spin Upkeep. Photo courtesy of UK National Archives

Filled with 3000kg of “Torpex”, or torpedo explosives of the type used in regular torpedoes, the Upkeeps were extremely powerful weapons – the average regular bomb was only 250kg. Even so, Operation Chastise proved that at least two were required to breach any of the steel and concrete dams.  In the end, only the first two dams were breached – the third, Sorpe, was made of packed earth rather than steel and concrete. It was also too enshrouded in fog for the aircraft to make successful attacks.

The Raid and the Calgarian’s Role

But to get in the situation where the Upkeeps could be dropped required that the aircraft actually find and reach the dams in the first place. This is where Calgarian navigator Harlo “Terry” Taerum played his indispensible role. Because it was necessary to fly at extremely low altitudes (lower than some treetops!) so as to avoid enemy radar detection, Terry could not use the usual points of reference for navigation. Armed with nothing more than a compass, stopwatch, map, the stars, and ground landmarks, Terry Taerum managed to bring Wing Commander Gibson’s Lancaster to the first dam right on time despite deviating slightly while crossing the English Channel. Once over the reservoir, Terry moved across the aircraft interior to the spotting position that would allow him to see when the fore and aft spotlights converged on the water, signifying the required 18m altitude required for successful Upkeep deployment.

The first aircraft to make the bombing attempt, Gibson’s Upkeep launch unfortunately failed – it exploded short of the dam. As each plane could carry only one Upkeep, Gibson’s Lancaster was now essentially useless for the mission’s objective. Some commanders may have taken the decision to turn for home, but not Guy Gibson.

Armed with just a plethora of machine guns located throughout the aircraft, Gibson flew his Lancaster alongside his fellow pilots as the latter made their Upkeep attempts. Flying distraction and attracting German anti-aircraft fire, Gibson’s heroic performance allowed his squadron mates to make successful attacks on the dam, though it did take three more attempts, only two of which succeeded – but that was sufficient.

The Möhne Dam after it was "busted" by 617 Squadron. Photo courtesy of UK National Archives.

The first dam destroyed, 617 Squadron flew on to Eder dam, the second objective. Gibson, with Terry Taerum navigating, once again took the lead during the journey. Despite the fog and awkward topography, the fact that the dam was undefended allowed the Dambusters to make several attempted runs before the parameters were reached. Once again, it took two Upkeeps to breach the dam, but it was successful.

The final Sorpe dam, however, proved very difficult to breach, both due to its earthen nature and the extremely foggy weather. Furthermore, due to various reasons, only three planes made it to Sorpe, and not all at the same time. This meant that although the first plane reached the target while it could still be seen, the subsequent aircraft arrived too late and encountered extreme fog, impairing or preventing successful drops. It should also be noted that the Sorpe attempts were very different from the first two dams: because of topography, the planes could only attack by flying parallel to the dam and dropping their Upkeeps as regular bombs. Consequently, the Upkeeps for the Sorpe dam were not spun as “bouncing” was not necessary. In any case, the Sorpe dam was not breached and remained intact.

Outcome – the “Successful Failure”

Upon their return home, 34 of the surviving aircrew were decorated in front of the King and Queen at Buckingham Palace on June 22. Gibson was awarded the Victoria Cross and our Calgarian Terry Taerum was awarded a Distinguished Flying Cross. They were greeted as heroes throughout England and North America – “mobbed for autographs”, in Taerum’s words.  

With two of three dams “busted”, the mission can be considered a 2/3rds success in the immediate tactical sense. It came at a high price, however – eight of the nineteen Lancasters did not return home, and 53 of the 133 airmen who took part in the raid died. Of these, thirteen were Canadian.  As well, several hundred Allied prisoners of war died when the ensuring flood hit cities and POW/work camps downstream. In total, approximately 1600 people died as an immediate result of the dams’ destruction.

Strategically, the quantifiable outcome was not as great as had been hoped. Immediately after the raid, Wallis, Upkeep’s designer, wrote that a blow had been delivered from which Germany could not recover for several years. Although many power plants and mines had been destroyed or damaged, the dams were fixed by September, just four short months after the raid. As early as late June, water and electrical output had resumed pre-raid levels. Part of the reason for this was the lack of follow-up raids by Bomber Command: Germany’s 7,000 temporary workers were able to make repairs free from harassment. As a result, the effect on the Ruhr Valley’s industrial output was nowhere near as great as the Allies had expected. Food production, however, was a different story - though not a primary objective, the floods did succeed in making the valley’s arable land unusable well into the 1950s.

Qualitatively, the effect the raid had on the Allies’, and particular the British, morale was considerable. As mentioned in the introduction, the preceding years of the war had taken its toll on the citizens of the British Isles. The Dambusters raid finally produced a result that was concrete, focused, and daring enough to tell to the general populace. Photos of the destroyed dams (taken by photo reconnaissance Spitfires right after the raid) covered the front pages of newspapers, dramatically and drastically boosting British morale. To British citizens, it would appear this was the turning point of the war – or at least the beginning of it, as the same period of time marked the beginning of the end of the Kriegsmarine U-Boat threat as the Allies developed the ability to completely provide air cover over the whole of the North Atlantic convoy routes.

Guy Gibson and Harlo “Terry” Taerum would, unfortunately, lose their lives on separate missions after the raid. Terry lost his on September 16, 1943, while on a raid against the Dortmund-Ems Canal – his Lancaster was hit by light flak while enroute at low level. Gibson perished almost exactly one year later, on September 19, 1944, on his return from a bombing mission in a Mosquito.

If you wish to learn more about the Dambusters, the Bomber Command Museum of Canada has an excellent collection of articles on the many Canadians involved in the raid and can be accessed here.

Today, only two Lancaster bombers remain in flying condition – one at the Canadian Warplane Heritage Museum in Hamilton, Ontario, and the other with the Royal Air Force’s Battle of Britain Memorial Flight.


One of two airworthy Avro Lancasters, this is the Canadian Warplane Heritage Museum's unit, photographed at the 2010 Abbotsford International Airshow. Photo credit: Timothy Choi

Our Intention is to educate Canadian Citizens so that they:

  • Appreciate the role of our military heritage in protecting Canadian interests, values and beliefs.
  • Understand the role our military history has had in shaping our country and the world.
  • Are inspired to be engaged and well-informed participatory citizens of Canada.
 join us and 
 make a difference