The M1911A1 (Colt)

The legendary Colt .45, showing the unique pistol grip safety.  It was a fearsome weapon to fire, especially for a conscript unfamiliar with firearms
The Colt 'Forty Five' seemed to personify the US Army - big, loud and powerful.  It had been designed to halt the drug fuelled charge of a Moro tribesman during the American involvement in the Philippines.  No one doubted its stopping power, but the heavy recoil posed a problem, especially for new recruits.
The Colt was a standard single action weapon, with both a slide  and a grip safety, the latter locking the action unless the grip was firmly held.  Three magazines were carried, one loaded and two in a twin belt pouch.  Issue was widespread, the Colt being carried by many infantrymen who served mortars and machine guns, and by all officers from the rank of Major and above.  Company officers, Captains and Lieutenants, were officially issued a Carbine, however many also acquired a Colt.
The Colt was also issued to certain British troops, predominantly airborne and commando units, in preference to the revolver.  It earned an enviable reputation for reliability in both world wars, and was not replaced in US service until the 1980s, and there are those who would still choose it over its 9 mm successor.
M3'Grease Gun'

The M3 'Grease Gun', nicknamed for its resemblance to the mechanics tool.  It could be adapted to fire 9 mm ammunition by replacing barrel, magazine and breech
The US Army began the war with the Thompson submachine gun, but became interested in the design process used to churn out the British Sten in such numbers.  This study resulted in the M3 which appeared during 1942.The M3 was greeted with the same enthusiasm as the Sten, and was nicknamed the 'Grease Gun'.  It fired the same heavy .45 cal round as the Thompson, but was far easier to produce.  The rate of fire was particularly slow, and there was no function to select single shots as in the Sten.  There were numerous design flaws which only showed up in combat, and refinements were constantly made culminating in the M3A1 which officially replaced the Thompson in 1944.
Ammunition issue is somewhat difficult to assess for the M3.  Most contemporary photographs show men wearing normal rifle belts.  I am reliably informed the reason for this was that Infantrymen carried their magazines in the General Purpose ammunition bag, no purpose made webbing being provided as the SMG was an 'irregular' item for them.  As a result, they could carry as many available magazines as would cram into the bag.  A five pocket magazine pouch was not available until after the war in Europe.  A three pocket pouch was used by Ranger and Airborne forces whose issue of the M1 and M3 was more routine.  In either case, at least six magazines, total 180 rounds, would seem reasonable.

M1A1 (Thompson)

The M1A1, simplified for mass production but still unable to meet demand, despite its overwhelming popularity.  The magazine is the 20 round version

The 'Tommy Gun' provided one of the most enduring symbols of World War Two.  It was derived from the M1928 which, thanks to Gangsters and 'G' men, gained worldwide notoriety in the pre-war years.
The original M1928 was slightly longer at 86 cm, and marginally heavier.  It was easily recognisable thanks to its pronounced fifty round drum magazine.  When war broke out, the British Army recognised the need for submachine guns, and ordered the M1928 from America.  When the United States entered the war, they too turned to the Tommy Gun.  It soon proved impossible to meet supply without amending the original design, so the weapon was simplified as the M1A1 detailed above. This eliminated the impressive but troublesome 50 round drum in favour of 20 or 30 round magazines.
It is a tribute to the design of the weapon that, even though both armies introduced lighter and simpler weapons to replace the Thompson, it was still to be found in action in allied hands on every front throughout the course of the war.

The Rifle Model 1903 (Springfield)

The M1903 Springfield

The M1903A4 sniper rifle, note the removal of the foresight rendered obsolete by the telescopic fitting
Officially, the M1903 was rendered obsolete with the adoption of the M1 Garand.  However, such was the need for rifles as the US Army expanded that the Springfield still had a valuable part to play in World War Two.  
Its most important arena early on was the Pacific, as it was used to equip the burgeoning Marine Corps who came second in line behind the Army for receipt of the M1.  Within the Army itself, it was retained in two very different roles.  Firstly, pending the development of a suitable grenade launcher for the M1 Garand, it was retained at the rate of one per Rifle Squad for antitank grenade use, while from 1943 onwards it became the weapon of the sniper, fitted with a Weaver telescopic sight as the M1903A4.  It could also be found in the hands of certain rear echelon troops in place of the M1 Carbine.
The standard rifleman's belt had ten pockets, each holding a pair of five round clips for a total of one hundred rounds.

The M1 Rifle (Garand)

The M1 rifle, the most reliable self loader of the era
With the adoption of the M1 back in 1932, the US Army became the first in the world to deploy a self loading rifle.  They were perfectly placed to manufacture millions of the type by the time war came, giving their soldiers and later Marines a terrific advantage in the field.
The M1 had several curious, and not all entirely welcome features.  To load, the bolt was drawn back and locked.  The weapon was fed by an 8 round clip which was pushed whole into the rifle.  The bolt was then released to chamber the first round.  When the first round was fired, the gas operated piston cleared and reloaded the chamber as described above.  When the last round was fired, the bolt locked open to the rear and the redundant clip was ejected.  A new clip was inserted, the bolt released, and the weapon was ready again.  What caused some concern was that there was no way to recharge the clip if there were just a few rounds left in; the weapon had to be emptied before it could be reloaded.  The eye-catching ejection of the spent clip could also compromise attempts at firing from concealment, though surely loosing off eight rounds may also have hindered matters.
But these were minor flaws in most circumstances.  The volume of fire produced by the average soldier was staggering.  And ironically, that was perhaps the greatest failing of the Garand.  While Britain and Germany sought out new machine guns for their rifle squads, America looked at the Garand and thought they did not need such things.  Yet as impressive as the M1 was, it took a great many to match the fire of a single German MG34/42, As a basic load, each soldier was issued ten clips, one carried in each of thepouches of the standard rifle belt.  Latterly, bandoliers containing six clips wereissued, allowing for anywhere between 80 and 128 rounds to be carried by the average soldier.
The M1 Carbine

The M1 Carbine managed to achieve a popularity unsurpassed in American use, despite its dubious ballistic performance 
The M1 Carbine is one of those peculiar weapons which does not quite fit into any existing category.  The US Army quickly recognised that it would not be possible to arm all its men with the Garand for sometime as production geared up.  Men in rear echelon roles were not first in line for the new rifle, but still needed something to defend themselves with.  The original M1903 bolt action rifle and Thompson sub machine gun were both too heavy to haul around along with mortar ammunition or the like, so a new weapon was sought.  The result was the M1 Carbine.
The carbine fired a much smaller and lighter round than the Garand, though of the same 0.30 in calibre.  The smaller round allowed a much lighter weapon which was fed from a detachable box magazine which held 15 rounds.  A larger 30 round box was introduced towards the end of the war.  The carbine replaced the pistol as the official armament of many ranks of officers and became almost standard among men serving heavy weapons such as mortars or artillery pieces.  
Several modifications appeared; the M1A1 with a folding stock for Airborne troops and the M2 which introduced fully automatic fire and the larger capacity magazine.  This latter item only arrived towards the end of 1944 and had a rate of fire of 750 rounds per minute.  The M1A1 folded down to 65 cm, but was slightly heavier at 2.8 kg.
The main criticism of the M1 concerned its ammunition, which was often found wanting to stop a determined man in battle.  It was neither a close range saturation weapon, like the sub machine gun, and was too underpowered to equal a rifle.  It was highly popular, but was not further developed after the war.

The M1918A2 (Browning Automatic Rifle)

The BAR was not capable of delivering the same volume of sustained fire as either the Bren or the German GPMG.  Nevertheless it remained highly popular among the troops
The first point to note regarding the BAR is that it was not a light machine gun.  There was no facility to change the barrel and the magazine capacity was noticeably limited.  The BAR had first appeared on the Western Front towards the end of the Great War, wielded as an early 'assault rifle'.  It remained in service thereafter and was regarded as little more than a supplement to the M1 rifle.
The BAR was a gas operated weapon which held a chamber in the round between firing.  The original M1918 had no bipod, this being added to the A2 version described above.  This model also deleted the single fire option in favour of two rates of automatic fire.  The absence of a barrel change meant that the danger of overheating could only be tempered by limiting fire.
Ammunition supply is difficult to estimate.  A six pouch belt holding twelve magazines was worn by the Automatic Rifleman.  In Marine Corps use the assistant rifleman carried a further twelve magazines, which with the loaded box totalled 500 rounds.  The US Army equivalent added a third member to the gun team.  The gunner most certainly carried thirteen magazines, but how many were added by his assistant and ammunition bearer I do not know.  If anyone reading this can enlighten me, please drop me a mail below.

The M1919A4 (Browning Light Machine Gun)

The M1919A4 was intended to be used at Company level with a large team to support it.  Parachute and Ranger units both used it at Squad level in preference to the BAR
The M1919A4 fulfilled the light machine gun role for US forces in the absence of a more appropriate weapon.  It is difficult to describe it as a light machine gun, as it was noticeably heavier than other examples and also needed a weighty tripod mount to fire from.
The M1919 used an air cooled barrel, which could be changed so a spare was carried.  It operated on the recoil system and chambered a round between firing.  In an effort to reduce weight for those troops issued the M1919 in lieu of the BAR (Rangers, Paratroops), a revised M1919A6 was developed.  This fitted a bipod in place of the tripod mount, and used a rifle type shoulder stock.  It weighed in at 14.7 kg and was longer at 135 cm, but remained otherwise unchanged.
Ammunition was carried in boxes, each packing a single 250 round fabric belt.  How many could be carried along with the other equipment needed depended on the size of the team serving the weapon, but at least 1000 rounds would seem reasonable.

M1917A1 (Browning Heavy Machine Gun)

An M1917A1 team assessing their field of fire.  The similarities between the Browning and the Vickers are obvious, both clearly showing their Maxim heritage
The M1917 had made its debut in the closing stages of World War One.  It remained in US service and was slightly modified as the M1917A1 described above prior to America joining the war in 1941.
In general appearance it was similar to the Vickers, and was to prove itself equally as reliable in action.  It had the same three man crew combination described above, plus the usual assortment of ammunition bearers, spotters and headquarters personnel.  In the Infantry it was transported by Jeep, while the Marine Corps lugged theirs on handcarts.  It was also mounted on many halftracks in Armored Infantry units while others fitted the M2 HB described in

60 mm Mortar M2

An indication of the men needed to keep a weapon like the 60 mm in the field.  Note the man second from right bedding the bipod legs in
The 60 mm mortar was one of the more useful light mortars to see service.  It was a normal 'drop fired' weapon issued on the scale of one per Rifle Platoon; in Infantry and Marine Companies they were grouped into a single section, while Airborne, Armored and Ranger units deployed them within the individual Platoons.  If it had one drawback it was the weight, which normally meant a five or six man Squad was required to carry weapon, mount and ammunition.  A cut down model, with no bipod and a spade plate saw some Airborne service.  The M19 weighed over 9 kg, but was not as successful as the standard model. 

Rocket Launcher, M1A1 (The Bazooka)

A watchful rifleman carrying his Platoon's Bazooka during the Normandy campaign, illustrating just how unwieldy the weapon was when not in action
The US Army entered World War Two with no serious anti armour weapon for its infantrymen.  A few Boys rifles had been procured for evaluation, but their sole claim to fame was that a handful were taken into the Pacific theatre by Marine units as bunker busters.  The Army had a hollow charge grenade, but no means of delivering it until a Colonel Skinner suggested his rocket launcher, which no one had at that point considered seriously.
The combination proved an immediate success and within a year of Pearl Harbor the Bazooka was arriving in frontline use.  It was a simple weapon comprising a hollow launch tube into which a primed missile was inserted.  The rocket was detonated electrically, igniting the propellant which launched the projectile down the tube, causing a notable exhaust signature which meant the weapon was less than discreet.  Danger was also to be found at the other end of the tube, as rockets could sometimes continue to burn after firing which required a wire mesh screen to be fitted to the muzzle.
The early model was supplemented by the improved M9 during 1944 and the M9A1 which could be broken into two halves for easier carrying.  They were both longer at 155 cm and heavier at 7.1 kg and the firing batteries were replaced by a generator.  Smoke and anti personnel rounds were also available.  But against tanks the advent of heavy German models reduced effectiveness, and while soft targets could be engaged at up to 300 m, armoured targets were limited to around 100 m, though penetration was improved to around 120 mm.  An upgraded 3.5 in weapon did not see service until well after the war had finished.  Yet the Bazooka provided the average Rifle Platoon with some hope of defeating a German Panzer and was equally well employed to reduce enemy strongpoints from Europe to the Pacific.

M3A1 Anti Tank Gun

US recruits examining the 37 mm M3A1 which was to see only limited Army service, but was retained by the Marine Corps throughout the war
The 37 mm was one of several allied weapons copied from the German Pak35/36 described below.  It received its first combat outing in North Africa where the Americans encountered the same frustrations as the British against the Panzer III 'Specials' and the long barrelled Panzer IVs.
To fill the gap the US Army adopted the unusual policy of buying a British weapon - perhaps the first time ever trade went west across the Atlantic.  They produced the 6 pdr gun as the 57 mm M1 and it remained in service with their Infantry and Armored Infantry units throughout the war as well.  More valuable support came from the 3 in (76 mm) M5 gun deployed by the Tank Destroyer units attached to Infantry Divisions.
But history was kinder to the 37 mm than to the British 2 pdr.  The US Marine Corps needed a light, mobile weapon it could deploy in the island campaign they were fighting in the Pacific.  The 57 mm was too heavy for the role, so the 37 mm was chosen.  It could be, and often was, manhandled across beaches and other shore obstacles.