An army was made up of several divisions with between 10000 and 20000 men in each division. There were several regiments in a division. The regiment had a distinct identity, sometimes with a long history. In each regiment there were a number of battalions. There were usually five companies in an infantry battalion, each of 100 to 150 men with about 5 officers.

An armoured (or panzer) division had several tank regiments, infantry, artillery, engineers for building bridges or demolishing obstacles and its own transport, medical, signals and servicing units, all following the tanks. The divisional commander led from near the front, controlling his forces by radio.

There were usually nine battalions in an infantry division, with one or more artillery regiments and battalions of tanks or armoured cars, engineers, transport and other services. Some infantry divisions were 'motorised'. Several divisions made up an army corps, two or three corps formed an army and several armies an army group.

The German tanks were called panzerkampfwagen ('armoured fighting vehicles'), or 'panzers' for short. (Panzer is the German word for 'armour'.) The Panzer Mark II was a very light tank which was used in large numbers early in the war. The PZ IV could maintain a good speed, had armoured protection and excellent firing power with its high-velocity 75 mm gun. It could 'stand off' and shoot at most enemy tanks from beyond the range of their guns. The PZ Ill, with thinner armour and equipped with only a low velocity 37 mm gun, had to get close to the enemy in order to fire, when its thinner armour could be holed. When a shot pierced a tank's armour, red-hot metal flew around inside, causing fires and explosions, called the 'brewup', and if the crew were not killed they would suffer terrible injuries. The PZ Ills and lVs were later given thicker armour and bigger guns. The Russian T34 tanks were more powerful than these panzers and in response the Germans produced what was called the 'second generation' of panzers: the Tiger, fitted with the highly successful 88-mm gun, and the Panther.

The British tanks in 1939 were either too slow such as the Matilda 'I' tank or they were simply too light. The British never caught rip with the Germans, although the Cromwell, with a 75-mm gun, proved successful. They had to depend mostly on American tanks, which were improved in the light of British experience. The American car industry produced the Sherman in great numbers-nearly 50000. At 33 tonnes, it was much lighter than the German 43 tonne Panther and 68 tonne Tiger, but the Americans had to ship their tanks overseas and most cranes could not lift more than 40 tonnes. The Americans hoped to swamp the enemy with numbers.

In modern warfare a great deal of oil and petrol is required for vehicles, aircraft and ships. Obtaining enough of these fuels was a constant worry for all the powers during World War Two.