stated that operational deception had to be "based upon the principles of activity, naturalness, diversity, and continuity and includes secrecy, imitation, demonstrative actions, and disinformation." The 1929 Field Regulations of the Red Army stated that "surprise has a stunning effect on the enemy. For this reason all troop operations must be accomplished with the greatest concealment and speed." Concealment was to be attained by confusing the enemy with movements, camouflage and use of terrain, speed, use of night and fog, and secrecy. "Thus 'in Soviet military art during the 1920s the theory of operational maskirovka was developed as one of the most important means of achieving surprise in operations.'" The 1935 Instructions on Deep Battle and then the 1936 Field Regulations place increasing stress on battlefield deception. The Instructions define the methods of achieving surprise as air superiority; making forces mobile and manoeuvrable; concealing concentration of forces; keeping fire preparations secret; misleading the enemy; screening with smoke and technical deception; and using the cover of darkness. In the 1939 Russian invasion of Finland, white winter camouflage was worn by Soviet troops. 1944 concept The 1944 Soviet Military Encyclopedia defines military deception as the means of securing combat operations and the daily activities of forces; misleading the enemy about the presence and disposition of forces, objectives, combat readiness and plans. It asserts that it contributes to achieving surprise, preserving combat readiness and the survivability of objectives. 1978 concept The 1978 Soviet Military Encyclopedia defines deception similarly, placing additional stress on strategic levels, and explicitly including political, economic and diplomatic measures besides the military ones. It largely repeats the 1944 Encyclopedia's concept, but adds that Modern doctrine Russian military deception is broadly equated with maskirovka, but other Russian terms are also used in the area, including the "fog of war", tuman voyny. Khitrost means a commander's personal gift of cunning and guile, part of his military skill, whereas deception is practised by the whole organization and does not carry the sense of personal trickiness; nor need the Russian use of deception be thought of as "evil". Indeed, Michael Handel reminds readers, in the preface to the military analyst David Glantz's book, of Sun Tzu's claim in The Art of War that all warfare is based on deception; Handel suggests that deception is a normal and indeed necessary part of warfare. The goal of military deception is however surprise, vnezapnost, so the two