Hitler's secret weapon

Germany's propaganda minister, Joseph Goebbels, dubbed the V1s and V2s the Vergeltungswaffen, or retaliation weapons. From June 1944 to March 1945, the V weapons tormented Londoners. Some 2,419 V1 flying bombs reached the city and claimed 6,184 lives and injured 18,000 people. Another 517 V2 rockets hit London, killing 2,700 people and injuring over 6,500 more. Although London was the main British target of the V weapons, other targets including Portsmouth, Manchester and Norwich were also hit.

Apart from the cost in lives and injuries, the V weapons struck at British morale in the final stage of the war. While Allied forces began to squeeze the life out of the Reich from east and west, Londoners started to feel that victory belonged to them. Then, from out of the blue, came Hitler's high-tech revenge.

The German army started experimenting with small rockets in the early 1930s, and large-scale research and development began in 1936. The strategy of using mass attacks with big rockets to win wars first caught Hitler’s enthusiasm in August 1941. The German army showed him a film of early tests conducted by their top rocket engineer, Wernher von Braun. Impressed by the footage and von Braun’s presentation, Adolf Hitler declared the rocket a “revolutionary development” in the conduct of warfare. He told the army chiefs that he did not want to waste the technological breakthrough in small pinprick attacks, but instead he wanted to defeat his foes with surprise attacks of thousands of rockets. However, setbacks to the army’s development programme and more urgent demands on the Third Reich’s limited industrial and scientific resources delayed the move to full-scale production until March 1943.

The army’s head of rocketry believed that he could force the British out of the war with a barrage on London of about 900 V2s a month over five months. Not to be outdone by the army in the race to win the war for Hitler, though, the Luftwaffe built a rival weapon, a jet-propelled flying bomb. This had an edge over the rocket because it was much cheaper and easier to build. The Luftwaffe believed that it could knock Britain out by hitting London with 1,500 flying bombs in only ten days.

Both weapons received Hitler’s backing and by the summer of 1944 Germany had two long-range bombardment systems primed for an all-out attack on the British capital.

Despite German efforts to conceal V weapons, secret intelligence revealed their existence to the British long before the first one struck London. Rumours about rockets reached London in 1939 and in 1942. However, the breakthrough came in March 1943, when two captured German generals mentioned heavy rockets in a conversation secretly recorded by British intelligence. Not long after that, the British deceived a third captured German general into revealing the secret when they allowed him to obtain a specially printed one-off copy of the Daily Herald that reported false news from Sweden about German rockets.

From now on the British pondered the threat of a rocket attack with anxiety. Early forecasts of the damage from a sustained rocket strike on London presented the government with the terrifying prospect of tens of thousands killed and many more wounded, as well as the full-scale evacuation of London. In response, the British chiefs of staff ordered that the intelligence effort, including photographic reconnaissance flights over the suspected German rocket research establishment at Peenemünde on the Baltic coast, should be stepped up. Prime Minister Churchill appointed his son-in-law, the permanent secretary to the Ministry of Supply, Duncan Sandys, to head an investigation of the threat and to recommend countermeasures.

Sandys’ inquiry prompted a heated debate among the government’s top scientific advisors. RV Jones, a senior scientific intelligence official at the air ministry, considered the threat to be very real. However, Churchill’s chief scientific advisor, Lord Cherwell (Professor Frederick Lindemann), believed that the incoming intelligence about long-range rockets was nothing more than a German deception to cover some other secret weapon.

The debate revolved around a technical issue. Lord Cherwell argued that a big rocket propelled by the burning of the cordite would need to contain the combustion in a body of steel, making it too heavy to take off. Other scientists, including Jones, countered that a rocket that burned liquid fuel could be built light enough to make it a practical weapon.

Explosive payload

As in so many intelligence disputes, both sides had a point. Cherwell doubted that the Germans would invest scarce scientific and industrial resources in long-range rocketry to deliver a relatively small explosive payload when fleets of bombers, or flying bombs, could do the job cheaply and efficiently.

Yet his critics were also right. Cherwell underestimated the German scientists’ ability to solve the immense technical difficulties of propelling a rocket by burning alcohol and liquid oxygen, because that was precisely what Wernher von Braun and his ingenious colleagues at Peenemünde were doing in 1942–43.

Meanwhile, the British intelligence machine searched for fresh evidence. Jones found persuasive clues from decoded German military radio traffic (‘Ultra’ intelligence), such as the deployment of radar units near Peenemünde, which he correctly assumed were there to track flight tests. Aerial photographs of Peenemünde taken by fast Mosquito aircraft showed that the station was being expanded, but nothing conclusive arrived until 23 June 1943. The analysis of photos taken of Peenemünde that day by the Royal Air Force’s photographic intelligence unit at Medmenham clearly showed rockets.

Over the next six months the evidence mounted. Photo-reconnaissance found a facility near Calais that a French secret agent claimed was a rocket site. Photo-reconnaissance of northern France discovered that the Germans were building dozens of odd looking ski ramp-like structures alarmingly pointing at London. In November 1943, Flight Officer Constance Babington-Smith, a brilliant photo interpreter at RAF Medmenham, spotted a peculiar small plane on a ski ramp (shown under the magnifying glass in the image on page 57) at Peenemünde that further study confirmed to be a flying bomb.

This development added urgency to Operation Crossbow, the campaign against the V weapons. The Sandys inquiry suggested defensive measures, including preparations to evacuate London, the building of additional shelter, plans to warn the press and to control the news to prevent panic, and some inventive ways to deceive the Germans about the accuracy of their aim once the attacks began.

Anxious that the rockets might be used to disrupt D-Day or that they would take such a horrific toll on Londoners that the invading Anglo-American armies would be forced to divert their operations to the capture of the ski ramps, the government also considered offensive actions. If the bombardment became intolerable, Churchill suggested retaliating with poison gas. His military chiefs, however, advised against the diversion of strategic bombers from the systematic destruction of the German war economy to a mere reprisal. Even so, the British decided to attack known production and launch sites to suppress the V weapons.

On the night of 17–18 August, RAF Bomber Command sent 596 aircraft to attack Peenemünde in a daring precision raid with 4,000-pound blockbuster bombs. In December 1943, Anglo-American strategic and tactical air forces also began a campaign against the V1 launch sites that in its first phase flattened nearly all of them.

By the summer of 1944, Operation Crossbow became a race between Allied efforts to locate and bomb V1 launch sites and German efforts to rebuild them and to find ever more clever ways to hide them. That cat and mouse game, which the Germans began to win, continued until the autumn of 1944, by which time the Anglo-American armies had overrun all the V1 launch ramps.

Ineffective campaign

Although senior air force commanders complained about the diversion of bombers to an increasingly ineffective campaign against the V1s, the bombing certainly helped to reduce the frequency of the launches. The first phase of Crossbow and the Peenemünde raid – which forced the Germans to relocate their rocket scientists and to assemble the V2s in underground tunnels – also helped delay the start of the attacks by several crucial months.

Yet, even if Crossbow had been less successful, it is doubtful that the intensity of V attacks would have threatened the Allied war effort. After all, Hitler wanted more than revenge from his secret weapons: he wanted to knock Britain out of the war. To achieve that goal, his planners estimated that they needed to pummel London with thousands of V1s and V2s a day, but the actual strike rate never exceed a few dozen. That was in part due to mechanical failures and British air defences. But the root cause was a lack of industrial capacity to mount the sort of massive surprise attack that Hitler imagined in August 1941.

Ultimately, Lord Cherwell was right. A rocket was a very expensive way to deliver a one-tonne bomb. The V weapon only delivered 0.23 per cent of the total explosives dropped on the Reich by the Allied bomber forces.

From that perspective, the German V weapons programme takes on an air of desperation. It was no coincidence that Hitler ordered the V2 into mass production just after the debacle at Stalingrad. Rockets and flying bombs were the products of an expiring German military-industrial complex. They served no purpose other than feeding Hitler’s illusion that the war could be won.

That the Allies won through vastly superior industrial and military resources, however, does not diminish Operation Crossbow’s success. Early warning gave the British time to adjust to the new threat. Air superiority gave them a tool with which to suppress it.

In February 1944, only eight months after photographic intelligence discovered the V2s, Churchill said that he felt “much easier” about the rockets. Hitler “would certainly try the weapon,” but thanks to good intelligence and air power, Churchill told his top advisors, we should not become “the slave of our fears”.

Joe Maiolo is a professor at King's College London and author of Cry Havoc: The Arms Race and the Second World War, 1931–41 (John Murray, 2010). He was an advisor on the recent BBC documentary Operation Crossbow.

The V weapons

During the Second World War German scientists and engineers made extraordinary advances in jet propulsion and rocketry that produced two new long-range bombardment systems, the V1 flying bomb and the V2 rocket. They were first used against London in the summer of 1944 in what the British called Hitler’s V weapons campaign – the V stood for vengeance.

The V1 was a 25-foot-long pilotless airplane with a wingspan of 18 feet and was armed with a one-tonne warhead. It was powered by a pulsejet motor to a speed of 360mph and a range of 155 miles. The V1 could be ground launched from a ramp with a catapult or, much less often, air launched from a bomber. Once airborne, the V1’s heading was maintained by a mechanical autopilot with a compass and gyroscope. Once over the target area, a small propeller fuse would shut down the pulsejet and the flying bomb would fall to earth.

The V2 was a 46-foot-long liquid-fuel rocket that weighed 12 tonnes. Mobile units fired the rocket from concrete launch pads. At launch the V2 would climb to a height of up to 100,000 feet and then lean towards its target. The rocket engine would shut down once the V2 achieved a pre-set velocity. It would then free fall along a ballistic trajectory to its target. The blast from the rocket crashing into the ground at supersonic speed augmented the destructive power of its one-tonne warhead.

This article was first published in the July 2011 issue of BBC History Magazine