The Bf 109D, which entered Luftwaffe service early in 1938, was produced as an interim type while awaiting the arrival of the definitive Bf 109E, and was withdrawn in 1940. It was powered by the carbureted Daimler-Benz DB 600Aa, rated at 986 hp for takeoff and 910 hp for combat at 13,120 ft, giving 298 mph at sea level and 357 mph at 11,480 mph at 11,480 ft. I assert without fear of contradiction that this put it in an entirely different class from any and all biplanes.

This is probably the biggest error in Green’s magnum opus; the Bf 109D did not have a DB 600 engine, but rather a Jumo 210 like the earlier models.

Quite so. In my concern to avoid Eric Lund’s skepticism regarding non-English authorities I confined myself to Green, who is characteristically very detailed, but not always correct.

Turning rather to Willy Radinger and Walter Schick, _Messerchmitt Bf 109: The World’s Most Produced Fighter from Bf 109 A to E_, Translation by David Johnson of _Messerchmitt Me 109: Das meistegebaute Jagdflugzeug der Welt Engewicklung, Erprobung und Technkik, Alle Varianten: von Bf (Me) 109A bis 109E_, Atglen, Pennsylvania: Schiffer Military History, 1999 (which does correctly identify the engine) we find a speed of 471 kph (= 293 mph) at 4 km (= 13,125 ft) given for the D (on p. 72). This would imply that the D model would have a very substantial speed advantage over biplane fighters, but not quite so vast a one as the E.

But your point is an interesting one, although some comparisons with the monoplane Soviet I-16s flown by the Republicans might be in order. And don’t forget the biplane Italian CR.32s which did reasonably well against the monoplane I-16s.

In short the whole biplane/monoplane debate in the mid-30s wasn’t as clear-cut as hindsight would have it. And the Spanish Civil War provided lots of evidence for both camps.

If one examines the experience of biplane-vs-monoplane combat carefully it will be seen that biplane victories are almost invariably a result of faulty doctrine on the part of the forces flying the monoplanes. It had been appreciated already in World War I that the faster fighter should avoid a turning fight with slower opponents but instead always confine itself to high-speed firing passes, followed by a breakaway (“blowing through the merge,” in modern terminology) and then using its superior speed to set up another pass on terms of tactical advantage. For reasons which need not detain us, the lessons of the earlier conflict had largely been forgotten by the late 1930s and many air forces were slow to recognize that there was more to fighter combat than good turning performance. This led many pilots to misuse the strengths of the monoplane fighter.

Generally, the first generation of monoplanes had roughly a 20% speed margin over the fastest biplanes. With proper tactics, this should have given the monoplanes something like a 10:1 loss-exchange ratio in one-on-one engagements, and at least 3:1 in many-on-many engagements. But such advantages can very easily be dissipated by employment of inappropriate doctrine.

If one thinks about it in modern energy-maneuver terms, it will be seen that the biplane must always have a substantially lower corner speed in its doghouse plot than the monoplane, implying a much shorter turning radius (assuming both aircraft have enough power to realize their full maneuver potential). This inevitably made a turning fight quite dangerous for the monoplane, since it would bleed off energy and find itself unable to get away from the more maneuverable opponent. Generally, the monoplane could “get out of Dodge” by using its superior acceleration to dive away from the fight, quickly reaching a speed that the biplane could not match, but pilots were often reluctant to do this for reasons of pride.

Will O’Neil