"The Spanish Civil War, which had afforded such a fortuitous opportunity for the Luftwaffe to try out its strength under actual battle conditions, served just as useful a purpose for the Soviet Air Force, and soon awakened the Red aircraft industry to the plain fact that it was falling badly behind the times. The standard Russian fighters sent to Spain, mainly I-15 and I-153 biplanes and I-16 monoplanes, held their own against the Heinkel He 51s initially supplied to the Legion Kondor, but proved to be outclassed in every way by the Messerschmitt Bf 109s later sent against them. The Russian SB-2 aircraft, the so-called "fast bombers" needing no fighter escort, turned out to have all the disadvantages of the Dornier Do 17s in the same class with none of the advantages of the German machines, and for reconnaissance the Russians could provide nothing better than the archaic R-5 biplanes. No dive-bombing ground support aircraft comparable to the German Henschel Hs 123 or Junkers 87 were available. By 1939, the Russian aircraft designers were showing the world that the lessons of the Spanish Civil War had been heeded. Lavochkin was introducing the first of his highly-successful LA series of single-seater fighters, soon to be followed by the even more famous LAGG series; Petlyakov's twin-engine PE-2 was about to enter service, and subsequently become one of the outstanding medium bombers of the Second World War; and Ilyushin had just designed the Il-2 Sturmovik ground-support aircraft later to prove unequalled in its class anywhere in the world."