Early 1945
Selective fire (capable of fully automatic fire)
30-round magazine or 15 standard issue
About 600,000 produced
Initially, the M1 carbine was intended to have a selective-fire capability, but the decision was made to put the M1 into production without this feature.
Fully automatic capability was incorporated into the design of the M2 (an improved, selective-fire version of the M1), introduced in 1944.
 The M2 featured the late M1 improvements to the rear sight, addition of a bayonet lug, and other minor changes.

Research into a conversion kit for selective fire began May 1944; the first kit was developed by Inland engineers, and known as the T4.
Inland was awarded a contract for 500 T4 carbines in September 1944.
Although the conversion was seen as satisfactory, the heavier 30-round magazine
put greater strain on the magazine catch, necessitating the development of a sturdier catch.
The slide, sear, and stock design also had to be modified.
On fully automatic fire, the T4 model could fire about 750 rounds per minute, but generated a manageable recoil.

Although some carbines were marked at the factory as M2, the only significant difference between an M1 and M2 carbine is in the fire control group.
The military issued field conversion kits (T17 and T18) to convert an M1 to an M2.
Legally a carbine marked M2 is always a machine gun for national firearms registry purposes.

These M2 parts including the heavier M2 stock were standardized for arsenal rebuild of M1 and M1A1 carbines.

A modified round bolt replaced the original flat top bolt to save machining steps in manufacture.
 Many sources erroneously refer to this round bolt as an 'M2 bolt' but it was developed as a standard part for new manufacture M1 and later M2 carbines and as a replacement part, with priority given to use on M1A1 and M2 carbines.
The slightly heavier round bolt did moderate the cyclic rate of the M2 on full automatic.

Despite being in demand, very few M2 carbines saw use during World War II, and then mostly in the closing days against Japan.
The M2 carbine was logistically compatible with the millions of M1 carbines in U.S. service, and offered longer range, better accuracy and better penetration than (pistol caliber) submachine guns like the M1 Thompsons and M3 Grease Guns.
Therefore, after World War II, the M2 carbine largely replaced the submachine-guns in U.S. service, until it was itself replaced by the M16 rifle.

The M2 model was the most widely used Carbine variant during the Korean War.
A detailed study of the effectiveness of the M2 in the war was assembled by S. L. A. Marshall.
He found that many troops complained on the lack of effective range of the gun, which allowed the enemy to get close enough to throw hand grenades.
A more detailed analysis showed however that most troops who complained actually tended to run low on ammo, because they fired their M2 on fully automatic too soon.
Troops who fired their guns on semi-automatic at distance generally complained less about the M2's effectiveness.
Generally, the more seasoned troops used the latter approach.
The carbine was usually given to second line troops (administrative, support, etc.),
who had little combat experience and also did not have much training in small-unit tactics, but who usually had to engage the enemy at some critical moment, like a breakthrough or ambush.
Marshall noted that almost all killing shots with carbines in Korea were at ranges of 50 yards or less.
It was unsurprising therefore that the M2 was a preferred weapon for night patrols.
The M2 was also used in the early stages of the Vietnam War by special forces, ARVN advisers, and air crews.

Contemporary authors have struggled to categorize the M2 carbine.
On one hand, it is more powerful than a submachine gun and is considered by some to be an assault rifle, even though it fires a projectile considerably less powerful than the StG 44's 7.92×33mm Kurz.
On the other hand, the M2 can also be considered a precursor of the modern personal defense weapon (PDW) concept, even though contemporary guns in that catego
Early 1945
Selective fire (capable of fully automatic fire)
30-round magazine or 15 standard issue
About 600,000 produced
Initially, the M1 carbine was intended to have a selective-fire capability, but the decision was made to put the M1 into production without this feature. Fully automatic capability was incorporated into the design of the M2 (an improved, selective-fire version of the M1), introduced in 1944.  The M2 featured the late M1 improvements to the rear sight, addition of a bayonet lug, and other minor changes.
Research into a conversion kit for selective fire began May 1944; the first kit was developed by Inland engineers, and known as the T4. Inland was awarded a contract for 500 T4 carbines in September 1944. Although the conversion was seen as satisfactory, the heavier 30-round magazine
put greater strain on the magazine catch, necessitating the development of a sturdier catch. The slide, sear, and stock design also had to be modified. On fully automatic fire, the T4 model could fire about 750 rounds per minute, but generated a manageable recoil.
Although some carbines were marked at the factory as M2, the only significant difference between an M1 and M2 carbine is in the fire control group. The military issued field conversion kits (T17 and T18) to convert an M1 to an M2. Legally a carbine marked M2 is always a machine gun for national firearms registry purposes.
These M2 parts including the heavier M2 stock were standardized for arsenal rebuild of M1 and M1A1 carbines.
A modified round bolt replaced the original flat top bolt to save machining steps in manufacture.  Many sources erroneously refer to this round bolt as an 'M2 bolt' but it was developed as a standard part for new manufacture M1 and later M2 carbines and as a replacement part, with priority given to use on M1A1 and M2 carbines. The slightly heavier round bolt did moderate the cyclic rate of the M2 on full automatic.
Despite being in demand, very few M2 carbines saw use during World War II, and then mostly in the closing days against Japan. The M2 carbine was logistically compatible with the millions of M1 carbines in U.S. service, and offered longer range, better accuracy and better penetration than (pistol caliber) submachine guns like the M1 Thompsons and M3 Grease Guns. Therefore, after World War II, the M2 carbine largely replaced the submachine-guns in U.S. service, until it was itself replaced by the M16 rifle.
The M2 model was the most widely used Carbine variant during the Korean War. A detailed study of the effectiveness of the M2 in the war was assembled by S. L. A. Marshall. He found that many troops complained on the lack of effective range of the gun, which allowed the enemy to get close enough to throw hand grenades. A more detailed analysis showed however that most troops who complained actually tended to run low on ammo, because they fired their M2 on fully automatic too soon. Troops who fired their guns on semi-automatic at distance generally complained less about the M2's effectiveness. Generally, the more seasoned troops used the latter approach. The carbine was usually given to second line troops (administrative, support, etc.), who had little combat experience and also did not have much training in small-unit tactics, but who usually had to engage the enemy at some critical moment, like a breakthrough or ambush. Marshall noted that almost all killing shots with carbines in Korea were at ranges of 50 yards or less. It was unsurprising therefore that the M2 was a preferred weapon for night patrols. The M2 was also used in the early stages of the Vietnam War by special forces, ARVN advisers, and air crews.
Contemporary authors have struggled to categorize the M2 carbine. On one hand, it is more powerful than a submachine gun and is considered by some to be an assault rifle, even though it fires a projectile considerably less powerful than the StG 44's 7.92×33mm Kurz. On the other hand, the M2 can also be considered a precursor of the modern personal defense weapon (PDW) concept, even though contemporary guns in that catego
M1 carbine