Ordnance BL Tk. L11A5 (120 mm)

The Ordnance BL Tk. L11 (120 mm) on the Chieftain Mk 10 gun mantlet.

Description

The Ordnance BL Tk. L11 is a British 120 mm rifled cannon derived from the Conqueror's L1A2 120 mm main gun. This powerful gun was meant to be used in the Chieftain series Main Battle Tank, in-game this cannon is present on the Mk 3, Mk 5 and Mk 10 variants of this vehicle. At time of production, the L11, firing armour-piercing discarding sabot rounds (APDS), was one of the most fearsome anti-tank solutions present in an Armoured Fighting Vehicle and thus, fulfilled its purpose to defeat the 60s Soviet armour.

Vehicles equipped with this weapon

• Chieftain Mk 3
• Chieftain Mk 5
• Chieftain Mk 10
• Khalid

General info

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Available ammunition

Penetration statistics
Ammunition	Type of warhead	Penetration @ 0° Angle of Attack (mm)
		10 m	100 m	500 m	1,000 m	1,500 m	2,000 m
Shot L15A3	APDS	298	296	288	277	268	258
Shell L31A7	HESH	152	152	152	152	152	152
Shot L23	APFSDS	410	408	405	400	390	380

Shell details
Ammunition	Type of warhead	Velocity (m/s)	Projectile mass (kg)	Fuse delay (m)	Fuse sensitivity (mm)	Explosive mass (TNT equivalent) (kg)	Ricochet
							0%	50%	100%
Shot L15A3	APDS	1,372	7.48	-	-	-	75°	78°	80°
Shell L31A7	HESH	670	17.34	0.1	4	6.53	73°	77°	80°
Shot L23	APFSDS	1,535	3.89	-	-	-	78°	80°	81°

Smoke shell characteristics
Ammunition	Velocity (m/s)	Projectile mass (kg)	Screen radius (m)	Screen deploy time (s)	Screen hold time (s)	Explosive mass (TNT equivalent) (g)
L34	670	17.1	20	5	25	50

Comparison with analogues

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Usage in battles

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Pros and cons

Pros:

• The APDS round has high penetrating power, able to defeat all but the most heavily armoured MBTs it encounters.
• Has access to HESH ammunition, being capable of overpressuring and destroying lightly armoured vehicles in a single shot.
• The L21A1 12.7 mm Heavy Machine Gun can be used alongside with the main gun to accurately rangefind targets for the HESH due to the similar ballistic performance of both rounds.
• Late vehicles (namely the Chieftain Mk 10) have access to APFSDS ammunition

Cons:

• Slightly less accurate than smoothbore counterparts
• HESH shells produce little spalling, making them impracticable to fight heavy vehicles

History

During the development stage of the main armament of the future FV4201 Main Battle Tank, several novel propellant systems were considered. One of those was most notably a liquid propellant compound which would have allowed the crew to vary the propellant amount for each shot and thus the ballistics of the projectile. However, this system was quickly found to be unfeasible after trials in 1953, and thus a bag-charge system became the favoured method. A 105mm gun using bag-charges was specified in 1954. At this time, the turret design of FV4201 allowed a limited amount of space, leading engineers to limit the length of ammunition components to 27 inches (68,58cm) as the maximum. This ruled out conventional one-piece ammunition such as usually found on contemporary tank guns like the 20pdr OQF Mk.I (84 mm) or the Soviet D-10T (100 mm). Separate bag-charge ammunition was chosen, dividing the ammunition up into three pieces: Projectile, Bagged propellant charge, and ignition primer in the form of a small magazine containing essentially blank rifle caliber rounds to ignite the propellant. From Chieftain to Challenger 2, this system was retained. Curiously, an attempt was made to achieve a proper seal in the gun breech using brass stub cases (as later used on the Rh120 L/44 (120 mm) and its US American derivative, the M256m which are ejected after every shot automatically as the rest of the casing is combustible. However, this could not be made reliable or safe at the time. The British solution designed 100% of the propellant charge to be combustible, so that as soon as the breech opens, a new shell can be loaded. It was claimed that this system reduces loader fatigue, as each individual component the loader has to handle weighs much less than the equivalent one-piece 105mm round.

The 120mm calibre was not set in stone from the start either. Twelve guns in calibres between 105 and 130mm were considered before 120mm was recommended for further development in December of 1955. This experimental gun, designated as 120mm X23E2/3 was estimated to be able to defeat 120mm of RHA at 60° at 2000 yards (The same layout as the glacis plate of the T-54 Mod. 1947 and 20mm thicker than on subsequent variants of the T-54 and T-55, all of which was yet unknown to the British before a T-54 could be gathered after the Hungarian uprisings in 1956). Using the HESH round, about 150mm of RHA could be defeated at any combat range. By comparison, the NATO standard 105mm L7 derivative guns used on Leopard 1 and M60 could only defeat the NATO standard medium target ( a T-54) at 1.250 yards, and could not reliably defeat the NATO standard heavy target ( a T-10) at any range.

The design of the X23 which in service became the L11 offers a fascinating insight into tank design procedures: It was found that most loaders were right handed and preferred to load using their dominant arm. This meant they are best positioned on the left of the turret so gunner and commander would have to be on the right. This in turn meant that the sights would be offset to the right of the barrel's bore, and therefore the rifling of the barrel had to have a clockwise twist in order to compensate. A mechanised ramming system was also experimented with, however it was unreliable and added even more weight to an already dangerously overweight vehicle. British Army loaders therefore resorted to "charge-ramming", using the bagged propellant charge to push the projectile all the way into the breech. Gunnery trials in July of 1962 impressed: At targets out to 2000m, the crews managed an 81% first round hit probability using APDS, proving the L11's accuracy.

Media

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See also

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• reference to the article about the variant of the cannon/machine gun;
• references to approximate analogues by other nations and research trees.

External links

References:

Britain tank cannons
30 mm	L21A1
40 mm	QF 2-pounder
47 mm	Ordnance QF 3-pounder
57 mm	6pdr OQF Mk.III · 6pdr OQF Mk.V
75 mm	OQF Mk.V
76 mm	OQF 3-inch Howitzer Mk I · OQF 3in 20cwt · QF 17-pounder
77 mm	OQF Mk.II
84 mm	20pdr OQF Mk.I
94 mm	28pdr OQF · 32pdr OQF · OQF Mk.II
95 mm	Howitzer, Tank No.1, Mk.I
105 mm	LRF · Royal Ordnance L7A1
120 mm	Ordnance QF Tk. L1A2 · Ordnance BL Tk. L11 · L11A5 · L30A1
165 mm	ORD BL 6.5in L9A1
183 mm	QF L4A1
	Foreign:
25 mm	M242 (USA)
37 mm	M5 (USA) · M6 (USA)
75 mm	M2 (USA) · M3 (USA)
84 mm	kan Strv 81 (Sweden)
105 mm	Sharir (Israel)
120 mm	Rh120 L/55 A1 (Germany)
125 mm	2A46M-5 (Russia)
155 mm	M185 (USA)
	South Africa
20 mm	GI-2
76 mm	GT-4
90 mm	GT-2
105 mm	GT-3 · GT-7 · GT-8
155 mm	G6 L/45