as the Type VII submarine and wolfpack tactics. Gradually, improving Allied technologies such as the Leigh light, hedgehog, squid, and homing torpedoes proved effective against German submarines. Land warfare changed from the static front-lines of trench warfare of World War I, which had relied on improved artillery that outmatched the speed of both infantry and cavalry, to increased mobility and combined arms. The tank, which had been used predominantly for infantry support in the First World War, had evolved into the primary weapon. In the late 1930s, tank design was considerably more advanced than it had been during World WarI, and advances continued throughout the war with increases in speed, armour and firepower. At the start of the war, most commanders thought enemy tanks should be met by tanks with superior specifications. This idea was challenged by the poor performance of the relatively light early tank guns against armour, and German doctrine of avoiding tank-versus-tank combat. This, along with Germany's use of combined arms, were among the key elements of their highly successful blitzkrieg tactics across Poland and France. Many means of destroying tanks, including indirect artillery, anti-tank guns (both towed and self-propelled), mines, short-ranged infantry antitank weapons, and other tanks were used. Even with large-scale mechanisation, infantry remained the backbone of all forces, and throughout the war, most infantry were equipped similarly to World War I. The portable machine gun spread, a notable example being the German MG 34, and various submachine guns which were suited to close combat in urban and jungle settings. The assault rifle, a late war development incorporating many features of the rifle and submachine gun, became the standard post-war infantry weapon for most armed forces. Most major belligerents attempted to solve the problems of complexity and security involved in using large codebooks for cryptography by designing ciphering machines, the most well known being the German Enigma machine. Development of SIGINT (signals intelligence) and cryptanalysis enabled the countering process of decryption. Notable examples were the Allied decryption of Japanese naval codes and British Ultra, a pioneering method for decoding Enigma benefiting from information given to the United Kingdom by the Polish Cipher Bureau, which had been decoding early versions of Enigma before the war. Another aspect of military intelligence was the use of deception, which the Allies used to great effect, such as in operations Mincemeat and Bodyguard. Other technological and engineering feats achieved during,