Draft:120mm M58 gun

120mm M58 gun
120mm M58 gun
	M58 tank gun mounted on M103 heavy tank
Type	Rifle gun
Service history
In service	1956-1974
Used by	US; UK; France
Production history
Designed	1945
Produced	1956
Variants	L1(conqueror) D.1203(AMX-50) T53(T34 heavy tank)
Specifications
Mass	6,280 pounds (2.85 tonnes)
Length	298.75 in (7.588 m)
Barrel length	282 in (7.2 m)，L/60
Shell	Separate loading charge and projectile 　 APBC・HE 120×833mmR HEAT 120×660mmR
Shell weight	48.8kg
Caliber	120mm
Elevation	+15°~-8°
Rate of fire	5 rpm
Muzzle velocity	1067m/s M358 APBC 1143m/s M469 HEAT-FS
Maximum firing range	23,125m

The 120mm M58 tank gun was a 120mm rifled tank gun developed by the U.S. Army in the early Cold War, and was primarily mounted on the M103 heavy tank.

The version produced under licence by the British Army was the Royal Ordnance L1 tank gun mounted on the Conqueror heavy tank, while the version produced under licence by the French Army was mounted on the AMX-50 as the D.1203. The M58 was replaced by the M68 105mm gun and the M256 120mm smoothbore gun. Despite its replacement, the M58 is the tank gun with the longest barrel length, heaviest weight and highest muzzle energy of any tank gun ever used in the U.S.Army.

Development

Development of the M58 tank gun began late in World War II. In early 1945, the U.S. Army Ordnance Department began to consider converting the M1 120mm anti-aircraft gun into a tank gun. The new tank gun developed there was named the T53 120mm tank gun and was tested on two T30 heavy tanks, known as T34 heavy tanks.The T53 tank gun fired a T14 armor piercing round with an initial velocity of 960 m/s and at close range it delivered 286mm penetration against vertical armor, which was greater than the T5E1 105mm tank gun mounted on the T29 heavy tank and the T7 155mm tank gun mounted on the T30 heavy tank. With the end of World War II, the T53 gun and the T34 heavy tank did not reach final production, but they served as the basis for heavy tank design.

In 1948, with the Cold War in full swing and the need to counter the Soviet Union's IS-3,T-10 heavy tanks and other heavy tanks with high defensive capabilities, the U.S. Army Ordnance Department proposed design specifications for a modernized heavy tank, which called for the new T43 (later M103 heavy tank) to be armed with a 120mm tank gun. The U.S. Army Ordnance Department approved the T123 tank gun as the basis for further development of the lightweight T53 tank gun, of which the T123 was selected as the main armament for the T43 heavy tank. Cold forging technology increased the maximum chamber pressure from 38,000 psi of the T122 to 48,000 psi, which in turn increased the muzzle velocity of the armor-piercing round from 960 m/s to 1,067 m/s when fired. However, due to delays in ammunition development, the T123E1 was not officially designated the M58 120mm tank gun until February 25, 1956.

Technical Features

The M58 tank gun was basically a modified World War II design, with a caliber of 120 mm, a barrel length of 60 caliber, and an overall weight of 2.85 tons.

The barrel was of single-layer construction with a self-bracing system and 42 rifling engraved at 1:25 pitch. The barrel was reinforced with chrome plating, but due to high chamber pressure and heavy wear, the gun had a short life of 250 rounds.

The front of the barrel had a smoke evacuator section, and early types had flame induction holes on both sides of the muzzle, but these were soon eliminated because they caused severe burnout; the M58 did not have a gun stabilizer, so it could not fire between marches, given that the main mission of NATO heavy tanks was to provide long-range fire support, This drawback was not noticeable.

User

U.S. Army

The M58 tank gun was the main armament of the M103 heavy tank and was fitted on all M58s except the first T43 prototype, which used the T122. Due to the excessive weight of the ammunition, two loaders were required: the first loader would load a 23 kg shell and then a 25 kg cartridge. The second loader would then push the shell and casing together into the chamber, and the closure would close automatically, an operation that required a high degree of skill on the part of the loader. This operation required a high level of skill on the part of the loader, because if it was not loaded correctly, a gap would form between the shell and the chamber, making it impossible to fire, and the loader would have to get out of the vehicle and use the clearing lever to remove the shell from the chamber. Therefore, the loaders of the M103 tanks took great pride in their work. With the help of the two men, the M58 was able to reach a maximum firing rate of five rounds per minute.

The M58 was also to be installed in two new heavy tanks that would replace the T43. The T57 heavy tank with an oscillating turret. An improved T123 tank gun (renamed T179) was fixed to the upper half of the turret, with a revolver autoloader for rapid-firing eight rounds of ammunition. The other tank was the T110 heavy tank, also using the T123 gun (renamed T204); the T43E1 restoration project was an immediate success and was designated as the M103 heavy tank, while the T110 and T57 projects were cancelled in September 1956 and January 1957, respectively.

The M58 had a lighter derivative, the T123E6, which reduced the overall weight from 2.85 tons to 1.93 tons. This tank gun, along with the M41 90mm tank gun, the 90mm T208E9 smoothbore gun, the 105mm X15E8 gun, and the 105mm T254 gun (the American variant of the L7), were put to the test to select the main armament for the next generation of medium tanks, with the T254 winning as the M68 tank gun and the T123E The T123E6 came in second due to its slow rate of fire. For more than 50 years since then, the U.S. Army's main tanks have all used licensed production versions of foreign-made guns, and the M58 was the last independently designed and mass-produced tank gun.

British Army

In 1949, the British Army was tasked with developing a tank with a 120mm rifled gun that would be powerful enough to counter the IS-3. It was therefore decided to convert the existing Centurion main battle tank into a heavy tank (i.e., FV214 Conqueror ), which would be equipped with a 120mm gun. In 1950, overcoming opposition from the military, the British government obtained a license from the U.S. to produce the M58 tank gun, It was named the Royal Ordnance L1 gun. Many optimizations were made to the M58 design in order to adapt it to the Conqueror design.

The barrel length was shortened from the M58's 60 caliber to 55 caliber, and the mounting position of the gun ears was changed to make effective use of space in the turret.

The closing mechanism was changed from the M58's vertical to horizontal, and an electronic control mechanism was adopted for the opening and closing operation to improve the loading speed and increase the firing rate.

The smoke evacuator at the front of the barrel was eliminated and a counterweight was added in the middle. Later the counterweight was replaced by a smoke evacuator, which became the L1A2 tank gun.

Ammunition could be shared between the L1 and M58 tank guns, but the British Army used its own proprietary APDS and HESH. Only one loader was assigned to the L1, and its maximum rate of fire was 4 rounds per minute. The L1 was once the most powerful tank gun in the British Army, and its performance was comparable to that of its successor, L11 gun. However, its large ammunition and excessive weight adversely affected its rate of fire. The L1 lost its significance with the introduction of the more manageable L7 and L11 guns, and the only British tanks that used the L1 gun were the FV 4004 and the Conqueror.

French army

After 1945, the French Army began to consider the introduction of 120mm guns for tanks, and the American T53 tank gun (the predecessor of the M58 mounted on the T34 heavy tank ) and the Royal Navy's QF 4.7-inch shipboard gun were among the candidates. The version with muzzle brake was known as the D.1203F, where F stands for frein de bouche (muzzle retraction device) The D.1203 gun was manufactured with a two-part barrel, was not equipped with a smoke evacuation system, and shared ballistic characteristics and ammunition with the M58. The D.1203 was mounted on the AMX-50-120 heavy tank, the latter having an automatic loading mechanism that could quickly fire six rounds of ammunition from the magazine.

In 1954, France fitted a modified version of the D.1203 into the AMX-50 B heavy tank. The barrel was molded in one piece, the barrel length was lengthened to 65 caliber, and a new T.O.B. (Tourelle Oscillante B) 120 turret was installed to increase the magazine capacity to 19 rounds, but the D.1203 was discontinued along with the AMX-50.

L1 mounted on conqueror
D.1203 mounted on AMX-50

Performance

Marine Staff Sergeant pictured with a HE used in the M58.

The M58 used a total of five types of shells: the M358 APBC, M469 HEAT-FS, M356 HE, M357 WP, M359E2 training round TPBC, and for L1, the British used the APDS and HESH for the L1.

The performance of the various guns is compared and shown below. In the penetrating power figures, the M58 is for armor inclined at 30 degrees, and the L1 and L11 are for vertical armor.


Type	M58		L1		L11
Shell	M358	M469	L1G	L31	L15	L23A1
Shell Type	APBC	HEAT-FS	APDS	HESH	APDS	APFSDS
Muzzle velocity（m/s）	1,067	1,143	1,433	762	1,370	1,542
Penetration （1,000 yard)	221mm	330mm	446mm	150mm	390mm	480mm
Penetration （2,000 yard）	196mm	330mm	N/A	150mm	N/A	N/A

References

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