Bombing Balance Sheet

by Maj Oliver Stewart
Editor of Aeronautics

British analyst compares bombing theories, methods and tonnage used in European war.

Factual information about the effects of Anglo-American bombing on German and German-occupied territory will continue to come in as Allied specialists study the ground and set their observations against the operational records of the bombing forces. But already a first assessment can be made of the power of incendiary, fragmentation and blast bombing and of the value of special bombs like those in the 12,000-pound and 22,000-pound categories.

All such studies must be concerned with relationships, the four main variables being the size of the attacking force, the type of bomb used, the nature of the target and the method of sighting and releasing the bombs.

It is almost useless to discuss any one of these variables without the others. Therefore no rational examination of Allied bombing results was possible until the Germans had surrendered and Allied specialists had visited the target areas. In the following remarks I use Air Ministry information plus data collected for me by two experienced observers who made a tour of northwest Germany.

I propose first to tabulate the official figures for the total bomb loads released. The tonnages are in long tons (one ton equals 2,240 pounds). I then propose to refer to target selection and to the bombs, sights and methods employed for some of the more important attacks.

Six Years of Bombing
  RAF  USAAF
1940  13,000 long tons   ……
1941  32,000 long tons  ……
1942  45,500 long tons  1,500 long tons
1943  157,000 long tons  48,500 long tons
1944  547,000 long tons  578,500 long tons
1945  191,000 long tons  263,000 long tons
Total  986,000 long tons  891,500 long tons

In the whole of the war in Western Europe the British and American air forces, excluding the Tactical Air Forces, dropped 1,877,500 long tons.

In the welter of statistics it is important to distinguish between the headings used. In the above table Royal Air Force Bomber Command and the RAF component of the Allied Air Forces in Italy are both included. Under the heading USAAF are included the 8th United States Air Force based on England and the 15th based on Italy.

Two points should be noted: first, it was not until the German bombing of Britain had been controlled (a result of the RAF Fighter Command victory in the Battle of Britain and the improvement in radar night location and fighting devices) that the RAF bomb loads began to increase rapidly; second, the rate of bomb loads was increasing much more rapidly with the United States than with the British forces. This was mainly owing to the greater productive powers of the United States but also partly because British production was to some extent hampered throughout by the need to disperse factories, to put some underground, to erect blast walls in the work- shops and generally to take precautions against the threat of enemy bombing.

Another point to be noted is that it was customary for the RAF to name a city as having been attacked when the chief targets, industrial plants, stores, railway marshaling yards and the like, were in that city. The USAAF, on the other hand, named only specific targets.

The consequence is that truly comparable figures for the "biggest" bombing attacks cannot be given. All that can be done is to quote some of the heaviest RAF attacks and refer to exceptionally large operations by the USAAF.

Here are two groups of bombing attacks by the RAF Bomber Command:

Bomber Command Attacks
High Explosive
Date  Place  Weight
June 6, 1944  10 Normandy
coastal batteries
  About 5,000 tons
October 14, 1944  Duisburg  Over 4,500 tons
March 11, 1945  Essen  About 5,000 tons
March 12, 1945  Dortmund  About 5,000 tons
Incendiary
    Number
February 13, 1945  Dresden  650,000
February 14, 1945  Chemnitz  730,000
March 7, 1945  Dessau  500,000

The weights or numbers of bombs dropped and the dates are noteworthy. The proportions of incendiary bombs to high-explosive by weight were judged by studying the target. The predominantly fire-raising attack on Dessau, listed above, resulted in the almost complete destruction of the whole area attacked. But more usually incendiaries are in the proportion of about 25% of the total load where a great deal of breaking up is necessary, to about 70% when the target proves to be of a highly inflammable nature.

Typical examples of incendiary proportions as used by the US Army Air Forces during 1944 are:

March 6………27% incendiary
March 8………70% incendiary
March 22………64% incendiary

So much for the general picture of the whole of the Anglo-American bombing offensive against German and German- occupied territory. We turn now to consider the bombs used, the special targets against which they were directed and the sighting and bombing methods which were developed during the European war.

Two main theories have been advanced regarding heavy bombing almost since bombing began. Both theories had adherents in 1939. The first was that precision bombing is possible; the second held that under active service conditions precision bombing is not possible and that all bombing attacks must therefore be considered statistically if they are to be properly evaluated.

At the beginning of the war the statistical theory was perhaps the more popular. A natural consequence was the view that the 250-pound bomb was the largest useful size for general purposes. It was better, according to this view, to cover a target area with a pattern of many small bombs than to try to obtain a direct hit with a few large ones.

Gyro-stabilized bombsights had been under development since 1917. But, although remarkably high accuracy was achieved with them in practice, accuracy decreased sharply under combat conditions. The vigor with which the heavy bombers were challenged by the German defensive fighters caused precision bombing to lose popularity.

The Bomber Command, which concentrated mainly on night work, introduced the so-called "tactical" bombsight, a simpler affair than the precision sights. They also cast about for simplified methods of bombing. Their efforts in the end led to the pathfinder technique.

The Pathfinder Force, with special navigational aids, was sent out to mark the target with colored pyrotechnics and it was upon these that the main bomber force concentrated.

The method was still mainly statistical. Even when the first ultra-large bombs came into use it remained so. The first of these ultra-large bombs were of the blast variety.

They were large canisters, not unlike the outside of the boiler of a railway locomotive, and they had a thin case. Their purpose was to initiate powerful shock waves in the air. Weighing up to 4,000 pounds they were found to be effective against many different kinds of buildings. The German cities testify to their power. Aachen, Julich, Düren, Cologne and other Rhineland cities were singled out by General Eisenhower as examples of massive damage. Krupp's now presents an area of two miles by one mile completely devastated. The 42 collieries, 10 synthetic oil plants and 22 marshaling yards of the Ruhr were neutralized mainly by blast and incendiary bombing attacks.

But the limitations of the big blast bomb were obvious from the beginning. Against underground factories they were all but useless. They could not dent the great concrete U-boat pens on the French Atlantic coast. They were incapable of destroying a viaduct, of destroying dams or deep oil storage tanks. They were ineffective against small specialized targets. It was on May 16-17, 1943, that the public first became aware that some highly specialized work had been going on with the object of improving the striking power of big weight-carrying aircraft. This was the date of the attacks by Bomber Command Lancasters on the Möhne and Eder dams.

It is still not permissible to describe the instrument used for blowing these huge concrete structures because it is likely to be required again in the war against Japan. But it can be stated that it was the first outward sign that a highly original mind had been working on the super-fortification problem — and arriving at some very satisfactory solutions.

B N Wallis devised both dam-busting equipment and the ultra-large, armor-piercing bombs — 12,000- and 22,000-pounders. They are high-velocity bombs that reach the speed of sound when dropped from about 15,000 feet.

Of high cross-sectional density, with ogival head, the big armor-piercing bombs are used with a bombsight developed at Farnborough. It was a further step forward in precision sighting from the Mark XIV bombsight with which most RAF squadrons were equipped and which was developed largely by Prof PMS Blackett and Dr Braddick.

The first use of the 22,000-pound bomb was on March 14, 1945, when it was launched against the viaduct at Bielefeld. It brought six spans down. The Altenbeken viaduct and the Arnsburg viaduct were also brought down with the 12,000- and 22,000-pound bombs.

Examination of the Arnsburg viaduct shows that two spans collapsed into the river Ruhr, though it is not certain whether the cause was a direct hit or the undermining effect of the large bombs on the viaduct's foundations.

The coming of these new bombs and new bombsights soon altered the aspect of statistical and precision bombing. Precision bombing gained significance. A new weapon had been created for big weight-carrying aircraft. And the aircraft itself had not undergone much change for it had been found that the ordinary Lancaster (with a few minor modifications, chiefly the removal of some defensive armament) could take the 22,000-pound bomb.

Bombing attacks now took on a new accuracy. U-boat shelters being built at Farge, near Vegesack, on the Weser, were attacked with the 22,000-pound bomb on the afternoon of March 27, 1945. They were broken up and the oil storage de- pot nearby was also badly damaged. The railway bridge across the Weser, near Bremen, was brought down. When we entered the city, the E- and R-boat shelters at Rotterdam, which had been attacked in December, 1944, were found to be badly damaged. In one place roofing had collapsed in an area of 120' × 38'.

These attacks called for a comparatively small force and were more militarily economical than the vast blast bomb attacks of the earlier period of the war. They culminated in perhaps. the greatest return for expenditure ever achieved in any single military operation in the whole history of war, the sinking of the 45,000-ton Tirpitz.

On November 12, 1944, thirty-two Lancasters set out for Tromsoe Fiord, each carrying one 12,000-pound armor-piercing bomb, and equipped with the precision bombsight. To give the bombs time to accelerate, the attack had to be made from more than 13,000 feet. Not only was the 792-foot Tirpitz sunk, but on April 9, 1945, the Admiral Scheer and on April 16, 1945, the Lützow were sunk by exactly the same weapons.

The bombing of the Dortmund-Ems Canal tells even more about improved precision and greater striking power, for it was one of the early targets for RAF bombers and also one of the last. On March 5, 1945, the Air Ministry was able to state that the canal was dry on both sides of the safety gates at Ladbergen, the fifth time the Canal had been drained by bombing.

Power of precision bombing had been amply demonstrated. Later attacks were made in daylight which were entirely different from the kind of blast and incendiary night attacks on which the Bomber Command had previously concentrated, but they would not have been possible had the German air force existed in strength at the time.

Consequently it may be said that the effectiveness of precision attack with large bombs was proved but that it became a possibility only after a high degree of air superiority had been secured by the Allies. In gaining that superiority the USAAF heavy bombers had been the major agent.

They had been pursuing their own, different, bombing policy with increasing energy since the moment the first Fortresses took off from an airfield in England to strike at Germany. They were using small and medium-size bombs and were achieving accuracy by working in full daylight and fighting their way through enemy fighter opposition.

Theirs was a dual purpose in that they ate into the reserves of the Luftwaffe by compelling the German fighters repeatedly to do battle on the largest scale and, at the same time, they damaged and destroyed specially chosen targets such as ball-bearing factories, fuel storage plants and railway marshaling yards.

Enemy oil stocks were rapidly reduced. Overall oil production was cut to 7½% of the April, 1944, output and aviation fuel production to 3½%. The launching sites of the V-weapons and the experimental stations where work was underway on multiple artillery, jet-driven aircraft and radar were also attacked and kept continuously behind schedule.

American heavy bombers had forced German aircraft to defend Germany and then had shot them down. The Russian front gained heavily from these bombing operations and by 1944 there were only 350 German fighters ranged against the Russians along a 2,000-mile front. American daylight bombing had drawn out the vastly greater part of the Luftwaffe's defensive weight. The destruction of enemy aircraft by the United States Army Air Forces, apart from the American Component of the Tactical Air Force, was almost entirely the outcome of these bombing operations. The enemy aircraft were either shot down by the bombers or by fighters escorting the bombers. The following table gives the claims from the beginning of the United States air forces operations until mid-April.

Enemy Aircraft Destroyed or Damaged
Organization  In the Air  On the Ground
8th Air Force  11,231  7,280
15th Air Force  3,949  2,342
9th Air Force  2,277  2,058
12th Air Force  2.913  220
Total  20,370  11,900

More remarkable — and more clearly the outcome of the work of the United States Army Air Forces (especially the 8th) — was the diminution in German air force strength. In the summer of 1941 Germany had 3,300 aircraft or 56% of the whole Luftwaffe, employed on cooperating with the German army. By the end of 1943 it had only 18%.

The RAF Bomber Command claimed 759 enemy aircraft destroyed, a figure which reflects the fact that the bulk of the RAF bombing was done at night and without fighter escort. The RAF Fighter Command figure of 6,977 is not directly related to the bombing operations.

After the Normandy landing, both British and American heavy bombers were called in at times to intervene on or very near the battlefield. A counterattack was stopped by this means at Villers Bocage on June 30, 1944, and the advance to the east of Caen in July was preceded by an attack by 1,056 Lancasters and Halifaxes together with 570 Liberators and 318 medium bombers.

Something must be added about certain special bombs used both by the Americans and the British. There are the fragmentation and anti-personnel bombs whose characteristic is that they have a flat scatter of fragments. They were used against airfields but mainly by the medium bombers.

Incendiary bombs were of many kinds. The RAF began with the conventional pattern, but in August, 1944, it introduced a new 30-pound incendiary bomb 21" long and 5½" in diameter. Its main filling is a solution of methane in gasoline under pressure. Descent of the bomb is controlled by parachute. On impact the striker of the bomb fires the detonator and its flash ignites the priming in a central tube. The priming ignites the thermite and this heats the interior of the bomb, raising still further the internal pressure.

Petrol is then forced through a flexible tube into a valve chamber through the outlet hole in the jet and through a hole in the bottom of the parachute container. As it passes out of the jet the petrol is ignited by the thermite flame from the vent holes in the striker housing. The jet of flame is about 15' long and lasts for two minutes.

This bomb was used against Munich on the night of April 24, 1944, by a force of 250 Lancasters. It was also used against Stuttgart and Bremen.

Jellied oil phosphorous and various kinds of cluster incendiary bombs have been used extensively by the Allied air forces. One American cluster bomb consists of 165 two-pound, 110 four-pound or 38 six-pound units. The cluster is broken at a predetermined height by a time fuse.

A rocket bomb has also been used by American aircraft for precision bombing from great heights with good armor- piercing effects. It is used with the Norden bombsight and has a supersonic impact speed.

The cost of the Anglo-American bombing operations against the Germans was 7,997 British and 8,062 United States bombers lost. Coastal Command, whose mine-laying operations may be held to be a part of the bombing offensive, lost an additional 454 aircraft.

The testimony of all who have visited Germany and inspected at close range the results of the Allied bombing confirms that it was a major factor in bringing victory and in reducing casualties of land and sea forces.

But heavy bombing is a highly complex military process. The aircraft, the bomb, the strength of the force employed, the sighting and dropping arrangements must all be related to the target. When all these variables are correctly related, heavy bombing can paralyze a country's war-making power.

This article was originally published in the September, 1945, issue of Flying magazine, vol 37, no 3, pp 21-23, 100, 101, 103-104, 106.
The original article includes 6 photos.
Photos credited to RAF, Charles E Brown, British Official, Photographic News Agencies.

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