Blitzkrieg, German for lightning war, was the original strategy of the German army during WWII.
Blitzkrieg worked in phases. First came a heavy bombardment by artillery. This performed two main tasks: it demoralised, depressed, and kept soldiers anxious; and secondly, it caused great damage by bringing down buildings, killing men, and wasting supplies. The second phase involved waves of fighter/bomber attacks. Usually these were bombing runs, designed to create weaknesses in the already hurt defences. Next, a large group of armoured vehicles would break through the weak points, and clear out the last vestiges of defence. Then, if needed, German shock troops would arrive via troop transport vehicles. The idea of the Blitzkrieg was to hit hard and fast, leaving no time to counter-attack. The attack was used in pairs, like pincers, to isolate a small area and consume it, amoebae-like.
In truth, the German Blitzkrieg was incredibly effective. The only way to counteract the brute strength of it was to rob it of its most valuable supply - surprise. The trick was to know where the Germans were going to strike, and to prepare in advance of it, to hit artillery with artillery, and meet air power with air power. But knowing where they would strike next was the real challenge, made difficult by a little device...
The Enigma Machine
The Enigma Machine served as the nerve centre of the Blitzkrieg. It was, at the time, the most advanced code generator ever created. This device consisted of a geared machine with three numeric dials, and a keyboard. As each dial's number was changed, the gears shifted positions, and a whole new code was generated. Every day a new setting was used, and this device effectively kept the Allied forces in the dark, allowing for orders to be sent in complete secrecy. The Allies needed to get their hands on the German Enigma Machine, and the movie U-571 was loosely based on this, though misrepresented. However, even with the Enigma Machine, the Allied forces had to be careful not to let on to the Germans that they had recovered one of these devices. This meant that only the most specific and dangerous raids would be prepared for. The Enigma Machine was changed and modified several times during the war, and through it, the Blitzkrieg found its might. Without prior knowledge of where the next blow would fall, the Blitzkrieg was practically unstoppable.
The Blitzkrieg was a brilliant tactic, overcoming the obstacles of WWI's problems with moving through trench warfare. To understand how effective it really is, one must realise that the Blitzkrieg is still used by nearly every army in the world today.