In the Pacific, where the Japanese tank threat was less significant, the M3 remained in service until the end of the war, but some 57mm guns were issued.

Like many other light anti-tank guns, the M3 was widely used in the infantry support role and as an anti-personnel weapon, firing high-explosive and canister rounds.

The inability of the 37 mm round to penetrate the frontal armor of mid-war tanks severely restricted the anti-armor capabilities of units armed with them.

Combat experience from Spain suggested that a light anti-tank gun, such as the German 37 mm PaK 35/36, was capable of neutralizing the growing threat posed by tanks.

[1] Another change was a threaded barrel end to accept a big five-port muzzle brake (gun M3A1, adopted on 5 March 1942).

[2][8] In an attempt to increase the armor penetration of the M3, several squeeze bore adapters (including the British Littlejohn adaptor) were tested; none was adopted.

[1] The barrel was of one-piece forged construction, with uniform rifling (12 grooves, right-hand twist, one turn in 25 calibers).

The telescopic sight on the M6 and both elevation and traverse controls were located on the left side, so one gunner was able to aim the gun.

According to their October 1942 organizational structure, an airborne division had 44 37 mm anti-tank guns: four in divisional artillery (AA/AT battery of parachute field artillery battalion), 24 in the AA/AT battalion, and eight in each of two glider infantry regiments; parachute infantry regiments did not have anti-tank guns.

The F-series TO from 5 May 1944 removed the special weapons battalion from the divisional organization, resulting in a total of 36 guns per division.

The gun was also supplied to Bolivia (4), Canada (3), Chile (198), Colombia (4), Cuba (1), El Salvador (9), France (130), Paraguay (12), United Kingdom (78), Soviet Union (63), Nicaragua (9), and other countries.

[18] Throughout the war it remained effective against Japanese vehicles, which were thinly armored and were rarely committed in large groups.

The light weight of the gun made it easy to move through difficult terrain; for example, when attacked by Japanese tanks on Betio during the Battle of Tarawa, Marines were able to heave the M3 over the 5 ft (1.5 m)-high seawall.

Its overall effectiveness and ease of use meant the gun remained in service with the Marine Corps and with some army units in the Pacific until the end of the war.

After the nearly disastrous Battle of Kasserine Pass in February 1943, reports from some of the involved units mentioned 37 mm projectiles "bouncing off like marbles" from the turret and front armor of German medium tanks and proclaimed the gun "useless unless you have gun crews with the guts to stand and shoot from 100 yards".

[11] The Army was initially uncertain if these reports reflected the obsolescence of the weapon, or whether unrefined tactics and lack of experience were to blame.

That day the 37 mm guns demonstrated once again both their effectiveness against pre-war tanks—when they helped to repel an attack by Italian Renault R 35s—and inability to cope with modern threats in a subsequent encounter with Tiger Is from the Hermann Göring division.

Nevertheless, the 82nd and 101st Airborne Divisions were reequipped with British-manufactured 6-pounder gun (57 mm) on carriage Mk III (designed to fit into the British Horsa glider) for the Normandy airdrops.

[8] At least in one case, Fifth Army Ordnance in Italy fitted the gun experimentally with fifteen 4.5 in (110 mm) aircraft rockets, in five clusters of three, mounted above the shield.

Those other pieces included the M1916 infantry gun of French design (these were later used extensively as subcaliber devices for heavy artillery.

The first, initially designated M3A1 but renamed M5 on 13 October 1939, was shortened by 5.1 in (130 mm) to avoid damage to the tube in wooded areas.

[49] In addition, the M3 on different pedestal mounts was mated to a number of other vehicles, resulting in an assortment of 37 mm gun motor carriages.

1943 Soviet analysis described armor-piercing shots as modern, but criticized the M63 HE shell, claiming its M58 base fuze didn't work properly in tests.