Familiarization with its construction, mastery [by Soviet pilots], and employment, based on the combat experience of 14th Guards Bomber Air Division and 4th Guards Air Corps
While he was visiting in the USA in 1941, M. M. Gromov gave an unflattering evaluation of the B-25 as a bomber. It is a pity that we do not know what he thought when he learned of the decision of the American government to deliver this same B-25, and not the requested B-17, to the USSR in lend-lease. But he could not have known that the first three B-25s transferred by the purchasing commission—B models—would become obsolete during the time of their journey from the American shores to the airfield of the NII VVS. By the summer of 1942, the manufacturer had begun production of the subsequent model of the aircraft—B-25C, which differed from its predecessor in having improved carburetors, heavier armaments, and installation of de-icing systems on the wings and tail. Delivery of the B-25C to the USSR had begun, the first aircraft being accepted by the 222d Bomber Air Division that was formed in the summer of 1942.
For Soviet aviators, the B-25s were quite extraordinary and an object of great interest. Special attention was given to the survival kit [NZ in Russian, “untouchable supplies”]. The Americans prepared this kit with consideration “for all eventualities of life”, so that in the event of an emergency the crew could survive, whether in the taiga or on a large body of water. “The survival kit contained even a fishing rod and canned worms,” recalled a flight commander in 125th BAP, V. A. Gordilovskiy, “but we never had a chance to go fishing.”
The first months of use of the B-25 brought unpleasant surprises to the aviators of the 222d BAD. It turned out that the aircraft was very demanding in regards to the quality of a landing strip after it had been repaired following enemy bombardment. If the nose wheel encountered a poorly filled and tamped bomb crater, it would pivot sharply and easily break. The aircraft ended up on its nose, which then led to further damage to the propellers and the navigator’s compartment. This B-25 would be out of action for some time.
Care had to be shown to the mechanism for warming the carburetors. The control lever did not have a stop, and if during takeoff in hot weather the pilot accidentally pushed the carburetor-warming lever forward, the fuel mixture would become over-enriched. The power output of the engine fell, there was insufficient takeoff field length remaining to rotate, and the whole matter frequently ended with damage to the aircraft.
In order to avoid this, the division maintenance personnel re-worked the throttles on the B-25 and mounted a so-called “gate” that fixed the “mixture quality” lever in the off position. Now this lever could be pushed forward only by inclining it to the side and releasing it from the disengagement notch.
“The engines suddenly began to miss. At first I blamed the mechanics,” recalled the 222d BAD engineer, A. M. Akvilyanov. “But when we flew along the ALSIB route, I understood what had happened.” It turned out that before starting the engines the ferry personnel pre-heated them with open flame—using burning gasoline in a barrel or branches in a bonfire. This, of course, simplified the process of warming the cylinder heads in field conditions, but the open flame also scorched the spark plug leads, which in the subsequent employment of the aircraft led to their cracking. At some later time, all of an engine’s cylinders would not fire during startup. The engine missed and did not develop full power.
Attempts to employ the signal rockets (flares) from the on-board equipment also led to problems. The rockets produced “double illumination”; PVO (air defense) fighters, not knowing about their American origin, attacked any aircraft giving these strange signals. Soviet-produced signal rockets had to be hurriedly delivered to the division.
Behind these annoying little things the big picture was materializing. The experience of the first months of employment of the B-25 in the division led to a conclusion that this bomber could be used also for flights to distant targets in the interests of ADD (long-range aviation). However, it was unsettling that during B-25 flights of modest range there were instances of damage that occurred during forced landings because of fuel expenditure problems. Until the receipt of recommendations on the appropriate employment of the aircraft and its components, five B-25s in a torpedo-bomber variant on-hand in the division were used temporarily for long-range flights. They were equipped with fuselage tanks that were hung in the bomb bay. The bombs themselves had to be hung on external hangers. The frontal area of this aircraft grew, increasing its fuel consumption and decreasing its operational radius below that which was required. “We gave thought even to ordering our pilots to fly to the distant targets with 650-gallon ferry tanks,” recalled V. A. Gordilovskiy, at the time commander of 1st Squadron of 125th BAP. “But because of the resistance they created, the expenditure of fuel grew so great that these tanks gave no advantage. Besides, it was not possible to monitor fuel flow from them.”
Similar measures were not considered to be the only way out. Not limited by complaints delivered to the manufacturer, division aviation specialists, having studied in great detail the equipment entrusted to them, saw possibilities for to improve upon it, and later directed their efforts to extract the maximum performance from the aircraft.
In 1942, the leadership of 222d BAD, with the cooperation of specialists from the Zhukovskiy Academy [Engineering Academy of the VVS] and NII VVS, focused their effort on determining the most appropriate regimes of employing the aircraft, improving its fuel economy, and studying the effects of carburetor heating on engine fuel consumption. The development of a table of most favorable flight regimes for various weather conditions and bomb loads was conducted under the guidance of M. S. Sklizkov. Depending on the specific mission, each crew received an individual table before takeoff.
On the insistence of the division engineering leadership, designers from Plant No. 156 developed a fuel cell that could be hung in the bomb bay, permitting the simultaneous hanging of four FAB-250 bombs (250-kg fragmentation bombs). The suggested fuel cell and a schematic of its mounting attracted the attention of American engineers for its originality. Airplanes equipped with them had better characteristics. Soon American production facilities began to manufacture these tanks and they became a mandatory item on B-25s being sent to the USSR. In addition, the Americans perfected its construction and mounted a sensor in it that reported fuel consumption.
Later, on the initiative of the division maintenance leadership, Plant No. 156 began to produce one-time-use fiber 220-gallon wing tanks. After their fuel was expended they were dropped. The mounting of auxiliary fuel cells permitted the duration of a bomber’s flight to be extended to twelve hours.
For the most rapid climb rate to the optimal altitude, the division began the practice of gaining altitude after takeoff by stages. On one occasion it was decided to confirm the economy of this method in comparison with the normal procedure, a continuous climb to altitude. It was discovered that using the conventional method, a B-25 consumed 25 percent more fuel than by the staged method.
Working to improve the operational and combat qualities of the aircraft, the division’s aviators successfully fulfilled the hitherto unknown to them function of test pilots. The division’s mechanics’ knowledge of the aircraft’s technical aspects permitted them not only to service the aircraft and apply modifications but also to become familiar with the behavior of the modified components in the air. K. S. Vartanyan, an engineer in the 125th BAP, was an example. He flew as the second pilot on 18 combat missions, independently evaluating the validity of the method of composition of the [flight regime] tables, substantiating to the doubters that the use of these tables in conjunction with other measures would lead to significant increases in the flight range and duration of the B-25.
The division’s efforts paid off: less than a year after its formation, on 27 March 1943 it received “guards” designation. Its 37th, 16th, and 125th Bomber Regiments were re-designated the 13th, 14th, and 15th Guards. The 4th Guards (formerly 222d) Bomber Division was transferred from Monino to Kratovo. The “newcomers” to Kratovo airfield encountered there the 45th Heavy Bomber Division (Pe-8), which had arrived from Ivanovo. Both bomber formations suffered from having to use the same airfield. Delays in takeoff were not permitted. Extra target runs and “wandering” might close the Kratovo runway for a B-25. Landing a B-25 at other airfields, though it was possible, was not desirable for several reasons: another airfield might not have any imported aviation gas on hand, and in the case of damage, it would lack the necessary spare parts. In addition, it was preferred not to land a B-25 on a “strange” unimproved airstrip: if the soil was not sufficiently firm, the aircraft simply might not be able to take off from this airstrip later (when fully loaded).
In this situation a tactical method of the division’s combat actions was born. In order to lay out a schedule of combat sorties and execute landings before the Pe-8s entered the air corridor of the Moscow PVO (antiaircraft defense) zone, extra passes over the target were prohibited. The attack would be made by all of the division’s aircraft on one target, in one pass, with one final run to target and navigator-bombardiers selecting individual aimpoints. It seems that this tactic would only serve to put all the B-25s at the mercy of German antiaircraft fires. In fact, it was quite to the contrary!
The division’s departure from the airfield (up to 40 and later up to 60 aircraft) was executed over a 35—40-minute period with established intervals between aircraft. The aviators who were based at Kratovo airfield accompanied this armada of aircraft, taking off into the night sky over such a short period of time, with happy rejoinders. But the enemy did not find the 4th Guards Division’s night bombing raids amusing. Thanks to the precise adherence to the flight schedule of each individual aircraft, the division’s time over the target was reduced to 15—25 minutes. Two aircraft released their bombs on the target each minute, a total of 8 or more 250-kg bombs on target. The characteristic feature of the work of B-25s was evenly distributed chains of deep craters. The plans of the German command were disrupted more than once.
This tactic required careful pre-flight preparation, the selection of the most favorable route to the target initial point, attentive analysis of the enemy’s PVO in the target area, and consideration for any changes in air defense tactics and an examination of methods to respond to these changes. Each post-flight briefing became in its own way a practical conference for the generalization of combat experience. No stone was left unturned, including the actions of German distraction groups: each occurrence of their dropping of an illumination flare over a false target (upon the approach of B-25s) or the dropping of bombs on our territory along the flight path of the B-25s. Even such minor subjects as the nature of the illumination of the German illumination bombs was discussed.
A thorough study of all the details of a combat sortie, both before it was flown and upon the crews’ return to the airfield, resulted in a sharp reduction in combat losses. Thus, in the 34th Guards Regiment (4th Guards Air Division) in 1944 one airplane was lost per 546 aircraft sorties flown. The low percentage of combat losses can also be attributed to the high thrust-to-weight ratio of the engines mounted on the B-25. It was not exceptional for an aircraft damaged by antiaircraft artillery fire to return to its airfield on one engine.
The guaranteed life of the R-2600-13 engine initially did not exceed 300 hours, but because of its reliability its life was extended. Later series of this engine (and later the R-2600-29) had a life of 500 hours. In mid-1943, because of a shortage of spare parts, the failure of new engines to arrive from the USA, and the poor quality of overhauls of the Wright-Cyclone in 138th SAM (Fixed Aviation Repair Shop) at Monino (after repair they failed more often), and also taking into consideration the fact that engines whose hours had expired continued to operate effectively, the decision was made to extend their use an additional 15—25 percent beyond the guaranteed engine life. This practice compensated for the lack of replacement engines for a time. It is interesting to note that even after exceeding guaranteed hours with added time, there were no complaints about their work.
The engines mounted on the B-25 did not perform well at high altitude. Having reached 3,000 meters, the pilot was advised to actuate the second speed of the supercharger. This characteristic of the B-25’s engines limited the aircraft’s combat ceiling. The airplane had to operate in the very “oven”, in the thickest belt of antiaircraft shrapnel. The working altitudes when bombing from a B-25 were from 1500—3000 meters (5,000 meters only when flying to targets with heavy antiaircraft protection, such as Danzig and Koenigsberg). If the situation permitted, bombs were dropped from 500—700 meters. In these conditions the aircraft survivability played a large role.
No doubts ever arose as to the durability of the construction of this airplane. Even when it had been turned into a sieve, the airplane flew. But the views of the manufacturer and the Soviet engineers on providing fire protection to the fuel cells were contradictory. In the end the aircraft maintenance leadership of the 4th Guards Division turned to deputy division engineer for ESO (electrical and special equipment) I. K. Sklyarenko, who oversaw the modification of the B-25 and A-20G at Plant No. 156, to organize there also the modification of the B-25’s fuel system. Engine exhaust gases were passed through filters (a set of serrated copper rings) and vented under pressure into the fuel cells, which reduced the danger of fuel system fires.
The defensive armaments of the B-25 also played a significant role in the return of aircrews to their bases. Although the Colt-Brownings had some characteristics that made them inferior to the UBT, on the whole the system of defensive armaments received passing grades from aircrews. The electric power control of the turret mounts permitted the gunner to concentrate all his attention on conducting fire at the enemy and not be distracted by the time and effort required to rotate the turret itself. The aiming sight had an adjustable illuminator that did not blind the gunner.
However, initially, on the early models of the aircraft, the defensive armaments could not be considered to be adequate. The lower turret was difficult to use. Before firing it had to be actuated smoothly (which is not possible in aerial combat) and completely to stop, otherwise during attempts to rotate it the electric motor that drove it would burn up. Observation of the lower hemisphere was conducted through a periscope mounted in the center of the turret, which for all its advantages had a substantial and uncorrectable deficiency—limited field of view. There was also dissatisfaction in the fact that when tracking the enemy aircraft with the barrels of the machine guns, the gunner, who sat immobile at the periscope, lost his spatial awareness of the fighter relative to the bomber, and in the event of a sharp maneuver of the enemy aircraft lost sight of it. This was the cause of the loss of more than one bomber. In connection with this, in the division they considered introducing a sixth member to the B-25 crew—an observer. On aircraft 41-12461 they examined the effectiveness of mounting a .50-caliber Colt-Browning machine gun in the tail blister. In aerial engagements they counted on the lower turret least of all. It was recommended to pilots who were executing daylight sorties that if enemy fighters appeared, they should drop down to 200 meters to prevent the enemy from “getting under the belly.”
Observations regarding the problems with the lower turret were turned over to representatives of the manufacturer (North American). They studied these observations, and with the B-25D-30 the lower turret was replaced by a tail gunner position and side machine guns in blisters. The aircraft was now more reliably protected from below and behind.
At the front the bomber demonstrated its suitability for flights in the worst kind of weather. On the evening of 28 January 1943, after a successful bombing mission on the railroad yards at Vyazma, the crew of V. A. Gordilovskiy (125th AP DD) landed at their airfield in an aircraft that was almost completely iced over. This successful landing was possible thanks to the excellent cooperation between ground personnel and the crew, the mastery of the aircraft commander, good flying qualities of the aircraft, and the fact that the aircraft had a de-icing system.
To break up the ice that formed on the wings during flight in clouds at low temperatures, the B-25, beginning with the –C model, used a de-icing system manufactured by B. F. Goodrich. Special three-chambered rubber boots were mounted along the leading edge of the wing, stabilizer, and rudder. Upon the introduction of air into the boots they expanded. The air subsequently passed through all three chambers, and as a result of their wave-like movement, the ice on the leading edge broke off. The airflow did the rest of the work. In addition, beginning with the B-25D, windshield wiper blades were installed for the cockpit Plexiglas of the pilots and navigator. To improve the effectiveness of these wipers, alcohol was applied to the Plexiglas. Before takeoff in bad weather, so as not to turn on the de-icing system, the ground crews carefully cleaned the ice off the aircraft. Subsequently, at the warm-up start, before taxiing out onto the runway, they washed the cabin glass of the navigator and if possible the surface of the Goodrich boot, in order to remove as many ice crystallization centers as possible.
Alcohol was also applied to the edges of the propeller blades in an effort to prevent ice formation. Of all the available de-icing systems, this had the greatest significance. Delay in activating the de-icing system of the propellers led to loss of power with all the consequences that resulted from that, and also to engine vibration. To ensure the smooth operation of the de-icing system, 100 liters of alcohol were carried on board the B-25.
The high electrical power-generating capacity of the Mitchell facilitated the installation of subsystems that lightened the crew’s workload during flight. The cabin warm air heater received good marks from aircrews. The B-25, in contrast to similar aircraft of its type manufactured in the Soviet Union, was equipped to keep the crew warm at altitude, even during the winter.
In general, the comfort level of the aircraft received heightened attention. For example, the American designers thought to install ashtrays and lighters in the pilots’ compartment for those who wished to relax after risking death over a target. However, in the Soviet VVS it was forbidden to smoke during a flight for a number of reasons. Relaxing was dangerous, a distraction of attention away from observation of the situation in the air—this might cost the lives of a careless crew. Smoking while drawing oxygen from a mask also represented a fire danger. A special order of 4th Guards Division prohibited smoking during flight, and therefore the crews hardly ever used the lighters and ashtrays on the B-25.
Of all the aircraft assigned to ADD, the B-25 had the most radio communications equipment. Long-range communications provided for contact between the crew and the ground. Its antenna was mounted on top of the fuselage. The B-25 also had a 50-meter trailing (reel) antenna for reliable long-range communications. In addition, the B-25 had three short-wave receivers and transmitters for conversations in the air between crewmembers, and also with a ground command post during taxi and flight in the airfield vicinity. Arrival at one’s own airfield was supported by an automatic radio compass. Navigators, who up to this time worked with the hand-tuned Soviet-manufactured RPK-2 radio compass, greatly appreciated the capability of the new device.
A qualitatively different level of training of radio repairmen was required to enable them to work on this more modern (than Soviet-manufactured) radio equipment. Specialists of the electrical and special equipment group were known in the division as “masters of all trades”, and therefore it came as no surprise that they assumed total responsibility for the function and repair of the turret electrical systems.
The function of the electrical components of the B-25 was supported by three electrical supply systems. The first supplied electrical energy to all users; the second, from one generator—to selected users; and the third, emergency, provided current from the batteries to 5—6 basic users—for ensuring communications with the airfield and landing the aircraft. In the first series of bombers the output of the on-board generator was 1.5 kilowatts. Subsequently, thanks to improvements, the total output of the two generators installed on the B-25 grew to 12 kilowatts.
The growth of the electrical power-generation capacity permitted additional energy-consuming accessories to be mounted on the bomber, in particular an air altimeter and electric autopilot Si-1.
The hydraulic autopilot A-3 was mounted on the first models of the aircraft. It worked satisfactorily, but our pilots were not pleased with the speed of transfer of the control yoke when the hydraulic autopilot was turned on. The electrical autopilot (already used on American heavy bombers) had not only great sensitivity to external impulses, but also could be linked electrically to the Norden M-9 bombsight, which enabled automatic bomb drop on the target. The autopilot was regulated in such a manner that before bomb drop the control of the aircraft was transferred to the navigator/bombardier. His course corrections automatically were transferred to the control yoke. Thus bombs could be dropped with a “jeweler’s precision”.
J models of the B-25, with electric autopilot that was linked to the bombsight, began to arrive in the USSR near the end of the war. In view of the fact that the aircrews were not trained in how to use the electric autopilot, and the maintenance personnel were not accustomed to servicing it, they sealed and covered the control panel for the autopilot on these aircraft.
At the end of November, 1944, three Soviet military specialists, among them the deputy chief engineer of 4th Guards Air Corps for electrical and special equipment, Major I. K. Sklyarenko, were sent on temporary duty to the USA for familiarization with the construction of the Norden M-9 bombsight and study of its combined operation with the electrical autopilot and instructions for use and repair.
“The sight was considered classified, and therefore the exercises with it were conducted in a special room without windows that was itself located in the center of an instructional building,” recalls Major Sklyarenko, “and in the store of the firm that produced the optics for this sight, it was displayed in a show window. This was the Americans’ version of ‘secrecy’.”
The program of instruction ordinarily lasted a year, but the Soviet specialists, who already at the beginning of training possessed a solid foundation in the subject, completed it in a little over three months. The next phase of the program included training flights. Major Sklyarenko flew six flights on a B-17 bomber at a USAAF training center in Denver, Colorado. On 2 May 1945, Sklyarenko’s American colleagues informed him of the impending victory in Europe. Soviet VVS B-25 crews began to use the Si-1 autopilot with linked Norden M-9 bombsight after the war was over.
The presence on the airplane of modern radio-navigational equipment conditioned the participation of 4th Guards BAK regiments in clandestine cargo and troop air-drop operations (or “special missions”, as these flights were recorded in pilot logbooks). Although less suitable for these air-drop missions, the B-25 was, nonetheless, an important participant. Crews of 4th Guards Air Corps flew 1,659 aircraft sorties delivering cargo to partisans in Czechoslovakia in March 1944. (For comparison, the crews of the regiments of our basic corps “trucks”, the Li-2, flew 430 aircraft sorties in the same period. ) With the installation of an 814-gallon fuel cell in the bomb bay, the B-25 could deliver 6—9 PDMM bags weighing 130 kg each to a drop zone in a single sortie. During the preparation of the bombers for these special missions, the external hatches to the navigator’s and gunner’s compartments were removed from the aircraft, and in their places were mounted shields that opened on hinges with the airflow. A portion of the bomb hangers were also removed and the cargo was hung in the bomb bay and secured with two ropes (or straps with extended buckles that had been made up for hanging 2000-lb. bombs) and one bomb shackle. One or two bags were also carried in the navigator’s compartment and another two in the photographer’s compartment. The B-25 crew could take a maximum of 12 bags on board. On these occasions, they could forget about any free space inside the bomber. When they reached the drop zone, the crew released the bags from the bomb bay and pushed them out the improvised hatches.
The possibility of reducing the revolutions of one engine without any risk to control of the airplane permitted B-25 crews to resort to tricks in order to deceive the enemy. Here is a case in point. On the night of 23 March 1945, the crew of Guards Major Pavkin received the mission to deliver two intelligence agents dressed in German officer uniforms to the outskirts of Berlin (12 km west of Ratenov). The first parachutist was dropped without incident. However, when the second parachutist was about to jump, a column of trucks appeared on the roadway below. The aircraft commander manipulated his engine throttles and propeller pitch controls in such a manner as to make his engines howl like those of a German aircraft, and circled around the drop zone for 40 minutes. When the roadway was clear, the “German officer” jumped into the night.
Among the agents delivered by B-25 into the enemy rear were people who had parachute training and others who had never been in an airplane before in their lives. Sometimes the size and shape of the parachutist made it difficult to drop him through the navigator compartment hatch at the proper moment. On these occasions the pilot had to hold the aircraft at a speed of 170 mph and jump altitude of not less than 300 meters.
In May 1945 the requirement came down to quickly organize the delivery of fuel and ammunition to the tank units of General Babadzhanyan, which were moving to liberate Prague. The 250th (formerly 34th) Guards Regiment of the 14th (formerly 4th) Guards Air Division was assigned this mission. Thanks to the foresight of regiment commander V. A. Gordilovskiy, the regiment had saved its 650-gallon ferry tanks. These tanks were filled with fuel for the tank units, and crates of tank ammunition were loaded into the bomb bays. The regiment’s heavily laden airplanes took off from Melets airfield and landed on a highway along which the tank units were moving. The tankers pumped their fuel from the aircraft into their vehicles with their own pumps. This was the second time during the war when a highway was used as a landing field, but it is virtually unknown.
In 1945, a large quantity (up to 1000 each) of the German Lotfe-7 gyroscopic reflector bombsight was discovered in a Karl Zeiss warehouse in the Soviet-occupied zone of Germany. The question arose concerning the possibility of using them in Soviet aircraft in conjunction with the Si-1 electric autopilot. The attraction to this sight was that it was sturdier in construction than the Norden. A test of the compatibility of the Lotfe-7 with the Si-1 autopilot was conducted on a B-25 of the 4th Guards Air Corps. This test was a failure. When the autopilot was turned on and the sight was adjusted for course, a significant shaking occurred that interfered with control of the aircraft and threatened to destroy the airframe. Even the assistance of a representative of the firm, a certain Doctor Kortum, and Major I. K. Sklyarenko from the 4th Guards Air Corps did not help in ascertaining the cause of this phenomenon, and the German sights remained “unemployed”.
The experience of the exploitation of the B-25 in Soviet aviation units was not wasted. After the war this experience was of great utility during the preparation for serial production of the Tu-4 strategic bomber. The specialists of the units that had fought with the B-25 (foremost of all—from the 4th Guards Gomel Air Corps) became irreplaceable consultants to the engineers of Moscow design bureaus. Much work had to be accomplished in the production of the electrical equipment of the AP-5 autopilot, which was similar in construction to the Si-1. For a long time they were unable to attain uniformity of the winding of the thin copper wire on the autopilot’s potentiometer. It never occurred to the workers that the smooth operation of the autopilot depended on the accuracy of their work. The prestige of aviation power had to be maintained by overcoming the attitude of poor quality. But that is another story.
The following persons assisted in the preparation of this material for publication: V. A. Gordilovskiy, I. K. Sklyarenko, M. S. Sklizkov, A. M. Akvilyanov, I. A. Shchadnykh, A. V. Dubakov, K. P. Ikonnikov, and A. V. Cherkasov.
translated by James F. Gebhardt
Photos from V.Emets archive via A.Pekarsh