With the reduction of German air power, oil became the priority target in the German economy. The bomber force for several months had been adequate for the task. A preliminary attack was launched on May 12, 1944, followed by another on May 28; the main blow was not struck, however, until after D-day. In the months before D-day and for a shorter period immediately following, all available air power based on England was devoted to insuring the success of the invasion.
Virtually complete records of the German oil industry were taken by the Survey. In addition, major plants that were subject to attack and their records were studied in detail.
The German oil supply was tight throughout the war, and was a controlling factor in military operations. The chief source of supply, and the only source for aviation gasoline, was 13 synthetic plants together with a small production from three additional ones that started operations in 1944. The major sources of products refined from crude oil were the Ploesti oil fields in Rumania and the Hungarian fields which together accounted for about a quarter of the total supply of liquid fuels in 1943. In addition, there was a small but significant Austrian and domestic production. The refineries at Ploesti were attacked, beginning with a daring and costly low-level attack in August 1943. These had only limited effects; deliveries increased until April 1944 when the attacks were resumed. The 1944 attacks, together with mining of the Danube, materially reduced Rumanian deliveries. In August 1944, Russian occupation eliminated this source of supply and dependence on the synthetic plants became even greater than before.
Production from the synthetic plants declined steadily and by July 1944 every major plant had been hit. These plants were producing an average of 316,000 tons per month when the attacks began. Their production fell to 107,000 tons in June and 17,000 tons in September. Output of aviation gasoline from synthetic plants dropped from 175,000 tons in April to 30,000 tons in July and 5,000 tons in September. Production recovered somewhat in November and December, but for the rest of the war was but a fraction of pre-attack output.
The Germans viewed the attacks as catastrophic. In a series of letters to Hitler, among documents seized by the Survey, the developing crisis is outlined month by month in detail. On June 30, Speer wrote:
The enemy has succeeded in increasing our losses of aviation gasoline up to 90 percent by June 22d. Only through speedy recovery of damaged plants has it been possible to regain partly some of the terrible losses.
The tone of the letters that followed was similar.
As in the case of ball-bearings and aircraft, the Germans took the most energetic steps to repair and reconstruct the oil plants. Another czar was appointed, this time Edmund Geilenberg, and again an overriding priority on men and materials was issued. Geilenberg used as many as 350,000 men for the repair, rebuilding, and dispersal of the bombed plants and for new underground construction. The synthetic oil plants were vast complex structures and could not be easily broken up and dispersed. The programs of dispersal and underground construction that were undertaken were incomplete when the war ended.
The synthetic oil plants were brought back into partial production and in remarkably short time. But unlike the ball-bearing plants, as soon as they were brought back they were attacked again. The story of Leuna is illustrative. Leuna was the largest of the synthetic plants and protected by a highly effective smoke screen and the heaviest flak concentration in Europe. Air crews viewed a mission to Leuna as the most dangerous and difficult assignment of the air war. Leuna was hit on May 12 and put out of production. However, investigation of plant records and interrogation of Leuna's officials established that a force of several thousand men had it in partial operation in about 10 days. It was again hit on May 28 but resumed partial production on June 3 and reached 75 percent of capacity in early July. It was hit again on July 7 and again shut down but production started 2 days later and reached 53 percent of capacity on July 19. An attack on July 20 shut the plant down again but only for three days; by July 27 production was back to 35 percent of capacity. Attacks on July 28 and 29 closed the plant and further attacks on August 24, September 11, September 13, September 28 and October 7 kept it closed down. However, Leuna got started again on October 14 and although production was interrupted by a small raid on November 2, it reached 28 percent of capacity by November 20. Although there were 6 more heavy attacks in November and December (largely ineffective because of adverse weather), production was brought up to 15 percent of capacity in January and was maintained at that level until nearly the end of the war. From the first attack to the end, production at Leuna averaged 9 percent of capacity. There were 22 attacks on Leuna, 20 by the Eighth Air Force and 2 by the RAF. Due to the urgency of keeping this plant out of production, many of these missions mere dispatched in difficult bombing weather. Consequently, the order of bombing accuracy on Leuna was not high as compared with other targets. To win the battle with Leuna a total of 6,552 bomber sorties were flown against the plant, 18,328 tons of bombs were dropped and an entire year was required.
Consumption of oil exceeded production from May 1944 on. Accumulated stocks were rapidly used up, and in six months were practically exhausted. The loss of oil production was sharply felt by the armed forces. In August the final run-in-time for aircraft engines was cut from two hours to one-half hour. For lack of fuel, pilot training, previously cut down, was further curtailed. Through the summer, the movement of German Panzer Divisions in the field was hampered more and more seriously as a result of losses in combat and mounting transportation difficulties, together with the fall in fuel production. By December, according to Speer, the fuel shortage had reached catastrophic proportions. When the Germans launched their counter-offensive on December 16, 1944, their reserves of fuel were insufficient to support the operation. They counted on capturing Allied stocks. Failing in this, many panzer units were lost when they ran out of gasoline. In February and March of 1945 the Germans massed 1,200 tanks on the Baranov bridgehead at the Vistula to check the Russians. They were immobilized for lack of gasoline and overrun.