Basically, there are three types of artillery: guns, howitzers, and self-propelled artillery pieces. Field guns are mostly employed in the direct fire mode to shoot straight at the enemy troops and vehicles as they include anti-tank guns, whose ammunition comes in one piece, with the loading charge and the projectile being contained in one casing. Howitzers, on the other hand, are used in the indirect fire mode, since they have a much higher angle of elevation, and their ammunition comes in two pieces: the propellant charge and the projectile, which are loaded separately into the breech.
In World War II, about 30% of the self-propelled artillery pieces were fitted with anti-tank guns and they were called 'tank destroyers', such as the German Nashorn or the American M18 Hellcat, featuring an 80mm and 76mm gun respectively. Today the anti-tank field gun has been replaced by the anti-tank guided missile, and the role of the tank destroyer is being played by the main battle tank itself. However, the majority of the self-propelled artillery were howitzers mounted on a tank chassis, which was powered by a powerful engine. Today, I dare to say that all of the self-propelled artillery are howitzers, whose crew are well protected by an armored domed turret, in which the howitzer is mounted. One of the most powerful self-propelled howitzers in the world is the Russian 2S19 Msta-S, which features a 152.4mm howitzer.
All three types of artillery are used so provide fire support to either the advancing spearhead infantry units or to cover an ordered retreat to regroup. Today, they are used in coordination with ground-attack aircraft and attack helicopters armed with anti-tank missiles and rockets to open breaches in the enemy lines. In World War II, the Wehrmacht made good use of the towed field artillery that were used together with the Junkers Ju-87 'Stuka' dive bomber to attack ground troops and destroy infrastructure. Some military historians called the Stuka the 'Blitzkrieg flying artillery'.
Below, the Russian 152mm field howitzer, which proved to be very lethal against the German infantry in WW2.
Below, the French 75mm field gun (Canon de 75), massively employed in World War I.
Below, the G6, a South African 155mm self-propelled howitzer.
