The word "biplane" literally means two planes or wings, from the Wright brothers first flight on December 17, 1903 in their biplane aircraft the Wright Flyer I, until a few years before WWII, the biplane literally ruled the skies. WWI saw the biplane rapidly developed from a simple mobile aerial observation and artillery spotting platform in to specialized war machines with dedicated interceptors, fighter-bombers and heavy bombers. Mono-planes and Tri-planes were tried by both sides in the fighter role in WWI with some successes but none remained in front line service for long, being replaced with biplanes as soon as improved aircraft designs became available.
Biplane Use Between WW1 and WW2
Between the wars the biplane became a mail carrier, passenger carrier and a play thing of the rich, this was in part due to the large number of surplus military biplane aircraft available at relatively low prices. Monoplanes had existed from a very early date but only became dominant with the introduction of new monocoque designs in the later part of the 1930's, up to this time the biplane was the best available aircraft design solution.
Biplane Service during WW2
By the outbreak of WWII most operational military aircraft in service were monoplanes, with the notable exception of basic biplane trainers, notably the Boeing Kaydet, Bucker Bu-131 Jungman and the de-Havilland dh82a Tiger Moth biplanes. Many civilian biplanes were eventually pressed into service with military forces during WWII but this was out of necessity rather than choice. One notable exception was the Fairey Swordfish biplane which remained the Royal Navy's main carrier born Torpedo bomber from 1935 until the end of WW2 regardless of the numerous attempts to replace it with newer biplane and monoplane aircraft designs.
Biplane Aircraft Production After WW2
After WWII ended many ex military biplane trainers were sold cheaply on the civilian market for use as trainers, crop dusters and personal private biplane aircraft transports. Biplane aircraft were still manufactured after WWII for special purposes, the American Pitt's Special was designed as an advanced aerobatic biplane aircraft and the largest single engine biplane, the Russian Antonov an-2 as a "land any-ware" flying truck primarily for agricultural use although due to it's outstanding STOL capabilities and ruggedness was used in considerable numbers by the Soviet armed forces for dropping paratroops.