Allied artillery doctrine is very advanced compared to their rival nations. They use their guns in direct support of front line units, with troops trained as forward observers. The massive firepower of their long ranged guns is able to be brought to bear with great accuracy and used to devastating effect against enemy units. This superiourity is taken further with US guns, self propelled artillery like the Priest and fearsome long ranged guns like the Long Tom can be used in great numbers thanks to the huge production and shipping capacity the US possesses.
The M1A1 Pack gun is a light howitzer designed to be able to serve in both an anti tank and infantry support role. In this sense it is a very versatile gun, able to be moved swiftly via a jeep and attack enemy units with indirect fire, then defend itself with direct fire when they counter-attack. It is very vulnerable to return fire and so it is a good idea to keep these guns screened with infantry or armour at all times.
The 17 Pounder was a pre-emption of heavier enemy armour. It has a very long range and devastating firepower able to defeat even the thickest enemy tanks. Even better, it can be dug into its surroundings to create a concealed position, perfect for defending a fixed position against an armoured enemy assault.
The Bofors 40mm is a British autocannon widely exported and used in many countries around the world. The gun is able to shoot explosive projectiles very rapidly and is deadly to low flying enemy ground attack aircraft and light bombers. It is essential to have a screen of these guns to protect marshalling areas from roving enemy aircraft. When pressed into attacking ground targets, the bofors is effective against all infantry and light vehicles, but its rounds will struggle to penetrate more than the lightest armour.
FlaK cannons are huge guns designed to lob projectiles high into the air to shoot down enemy bombers. As such they can engage enemy strategic bombers with moderate success, although should definatly be supported by fighters. Their huge range and velocity makes them very potent when pressed into an anti-tank role. As such they are often used to form ad hoc anti-tank positions. They can shoot enemy tanks at long range and with great power. Late in the war the 90mm FlaK cannon would gain a new role providing the primary armament on the M26 Pershings.
4.5 inch guns modernise British artillery bringing them up to date from their Great War 60 pounders. They can be towed by the universal carriers and used to bombard the enemy from long range. They have exceptional fire power and a low cost but are unweildy and cumbersome to move. They are best used defensivly where the enemy will come within their range, or to displace an enemy from a defensive position and pursuit is not the primary objective.
The M2A1 is a light field howitzer capable of sustained fire for long periods. It is pretty powerful but best used in large numbers to maximise the effect of their fire before the enemy realises what is happening and moves away from their target zone.
The 155mm Long Tom is a huge weapon capable of firing with great accuracy over extreme ranges. Its huge projectiles cause terrible damage to their target zone while the incredible range allows them to be deployed far behind the front lines, away from danger and retaliation, or to reach deep into enemy territory, smashing their marshalling areas and leveling their tanks before they can even enter combat. It is with weapons such as this that the Allies extensive spy network is so useful, infiltrating enemy territory and finding the most vulnerable targets for the artillery corps' guns.