135 mm/45 O.T.O. Mod. 1937 (135 mm)

Stern port battery of 135 mm/45 O.T.O. Mod. 1937 on RN Etna

Description

135 mm/45 O.T.O. Mod. 1937 was an Italian naval gun designed as a response to the French 138.6 mm/50 and was planned to be used on a wide variety of warships - from destroyers to battleships. Most of these planes were cancelled before completion, as the gun was introduced on the verge of WW2, and didn't see any major naval engagements before the armistice.

In the game, it's best used against destroyers and coastal vessels, as it features few characteristics that make it excellent in that role. Against cruisers, it will, however, suffer significantly from having a relatively low explosive filler.

Vehicles equipped with this weapon

General info

The gun is available in 4 different mounts. A single mount used on destroyers has the most rudimentary anti-fragmentation mount. Twin cruiser mount has insufficient protection to stop anything but the machine guns. Battleship secondaries come in two distinct mounts, and while both have a nearly identical armor, the twin-mount used on Cavour is somewhat more difficult to penetrate due to having a much smaller face and a side armor at a very steep angle.

Ship	Guns per mount	Front		Sides		Top		Elevator
Ship	Guns per mount	Thickness (mm)	Type	(mm)	Type	(mm)	Type	(mm)	Type
RN Conte di Cavour	2	120	RCA	80	RCA	60	RHA	100	RCA
RN Duilio	3	120	RCA	80	RCA	60	RHA	100	RCA
RN Etna RN Attilio Regolo	2	20	RHA	6	RHA	6	RHA	0	—
RN Comandante Margottini	1	12	AfA	12	AfA	12	AfA	0	—

Available ammunition

135 mm APHEBC Perforante shells pictured in-flight, with the aft battery of RN Etna firing in the background. Note the white tracer characteristic for armour-piercing shells.

The choice of shells is typical for the Italian pre-WW2 guns, limited to HE and AP against surface targets and HE-TF against aircraft. It's adequate for nearly every situation a warship can encounter.

135 mm HE Dirompente - Universal high-explosive round, great against frigates and torpedo boats alike, to a degree also useful against enemy destroyers, or to ignite heavier warships on fire.
135 mm APHEBC Perforante - The shell of choice against enemy cruisers, or to reach the ammo racks on destroyers. It lacks penetration to deal with some of the heavy cruisers or all of the battleships/battlecruisers, so against them the HE rounds would be a better choice.
135 mm HE-TF Contro-aerea - Time-fused high explosive shell, able to counter enemy aircraft through shrapnel. Use Distance fuse set accuracy crew skill to increase the probability of fusing in the perfect spot for the kill - however, even with the skill maxed-out, shells still can explode ± 100 m away from a target at 5000 meters range, which is more than enough for the aircraft to avoid taking any damage. Still - it's by far the best round to use against enemy airplanes.

Penetration statistics
Ammunition	Type of warhead	Penetration @ 0° Angle of Attack (mm)
Ammunition	Type of warhead	1,000 m	2,500 m	5,000 m	7,500 m	10,000 m	15,000 m
HE Dirompente	HE	23	23	23	23	23	23
APHEBC Perforante	APHEBC	171	139	100	73	56	45
HE-TF Contro-aerea	HE-TF	23	23	23	23	23	23

Shell details
Ammunition	Type of warhead	Velocity (m/s)	Projectile mass (kg)	Fuse delay (s)	Fuse sensitivity (mm)	Explosive mass (TNT equivalent) (kg)	Ricochet
Ammunition	Type of warhead	Velocity (m/s)	Projectile mass (kg)	Fuse delay (s)	Fuse sensitivity (mm)	Explosive mass (TNT equivalent) (kg)	0%	50%	100%
HE Dirompente	HE	825	32.42	0	0.1	1.8	79°	80°	81°
APHEBC Perforante	APHEBC	825	32.73	0.01	6	1.47	48°	63°	71°
HE-TF Contro-aerea	HE-TF	825	32.42	0	0.1	1.8	79°	80°	81°

Comparison with analogues

135 mm is a fairly unusual calibre, thus the comparison will be made with the guns of relatively similar calibre used as either primary guns on cruisers, or secondary guns on battleships/battlecruisers. Pure destroyer guns are intentionally skipped.

HE

Cannon		Sample Ship	Ammo	Calibre (mm)	Muzzle Velocity (m/s)	Sustained rate of fire (rounds/min)	Targeting speed (°/s)		TNT Equivalent (kg)	Penetration @ 0° Angle of Attack (mm)
Cannon		Sample Ship	Ammo	Calibre (mm)	Muzzle Velocity (m/s)	Sustained rate of fire (rounds/min)	Horizontal	Vertical	TNT Equivalent (kg)	1,000 m	5,000 m	10,000 m
	135 mm/45 O.T.O. Mod. 1937	RN Etna	HE	135	825	7.5	9.5	9.5	1.8	23	23	23
	5 inch/38 Mk.12 (127 mm)	USS Atlanta	HE	127	792	15	21	13	3.22	36	36	36
	150 mm/45 SK L/45 (150 mm)	SMS Elbing	HE	150	835	7	4.2	4.2	1.6	21	21	21
	130 mm/55 pattern 1913 (130 mm)	Imperatritsa Mariya	HE	130	823	8	3.4	3.4	3.9	37	37	37
	140 mm/50 3rd Year Type (140 mm)	IJN Sendai	HE	140	840	6.2	8.0	8.0	3.15	35	35	35
	138.6 mm/55 model 1910 (138.6 mm)	Lorraine	HE	139	840	6	4.2	4.2	4.41	36	36	36

AP/SAP

Cannon		Sample Ship	Ammo	Calibre (mm)	Muzzle Velocity (m/s)	Sustained rate of fire (rounds/min)	Targeting speed (°/s)		TNT Equivalent (kg)	Penetration @ 0° Angle of Attack (mm)
Cannon		Sample Ship	Ammo	Calibre (mm)	Muzzle Velocity (m/s)	Sustained rate of fire (rounds/min)	Horizontal	Vertical	TNT Equivalent (kg)	1,000 m	5,000 m	10,000 m
	135 mm/45 O.T.O. Mod. 1937	RN Etna	APHEBC	135	825	7.5	9.5	9.5	1.47	171	100	56
	5 inch/38 Mk.12 (127 mm)	USS Atlanta	SP Common Mk.46	127	792	15	21	13	0.9065	150	95	56
	150 mm/45 SK L/45 (150 mm)	SMS Elbing	APCBC	150	835	7	4.2	4.2	0.99	238	153	93
	130 mm/55 pattern 1913 (130 mm)	Imperatritsa Mariya	SAPBC	130	823	8	3.4	3.4	1.67	178	115	71
	140 mm/50 3rd Year Type (140 mm)	IJN Sendai	mod 1 SAP	140	855	6.2	8.0	8.0	2.21	115	81	54
	138.6 mm/55 model 1910 (138.6 mm)	Lorraine	SAPBC	139	790	6	4.2	4.2	2.93	73	47	34

Usage in battles

The biggest weakness of this gun largely determines its use. The low explosive filler makes it less effective to deal with cruisers than it might appear after reading the penetration table. Thus, it's particularly good at dealing with enemy destroyers and coastal vessels, while struggling to score kills on heavier warships.

Pros and cons

Pros:

Good rate of fire
High muzzle velocity
Sufficient penetration to counter any light cruiser and even some of the heavy cruisers

Cons:

Very small explosive filler of the HE and HE-TF shells

History

Originally designed in response to the French 138.6 mm/50, the 135/45 was initially planned to be introduced first with the Capitani Romani class in order to counter French large destroyers (contre-torpilleur), but after the outstanding performance of the guns they got recommended for the 1937 refits of the Duilio-class. They proved to have a lower dispersion than even the latest of the 120 mm guns, while having a higher maximum range and larger explosive filler.

During the war, a new single-mounts were developed for the Comandanti M. d'Oro-class. Only one hull of the class - RN Comandante Margottini - was launched, unarmed, to make space in the shipyard. The guns were instead planned to be used on the Yugoslav destroyer Dubrovnik, but the plan didn't come to fruition before the armistice in September 1943. Similar fate met the guns planned for aircraft carrier Aquila and cruisers Etna and Vesuvio. Finally, before the armistice, the refit of the Conte di Cavour was already in progress, with some of the 120 mm guns being already replaced by the twin 135 mm turrets.

The single-mount guns were also used for coastal defence since early 1943, primarily on the north coast of Sardinia.

During the Cold War, a new, fully automated anti-air mount was designed for the refit of the Giuseppe Garibaldi, but never seen any other use outside the one-off cruiser.

Media

Excellent additions to the article would be video guides, screenshots from the game, and photos.

External links

[Wikipedia] 135 mm/45 Italian naval gun
[NavWeaps] 135 mm/45 (5.3") Models 1937 and 1938
The Weapons of the Italian Ships (Le armi delle Navi Italiane) by Erminio Bagnasco, page 35 - 37
From Glasgow to Genoa under three flags – the Yugoslav flotilla leader Dubrovnik by Zvonimir Freivogel, page 87

Italy naval cannons
20 mm	20 mm/65 Breda · 20 mm/70 Oerlikon 3S · 20 mm/70 Scotti-Isotta Fraschini mod.1939
37 mm	37 mm/54 Breda Mod.32 · 37 mm/54 Breda Mod.38 · 37 mm/54 Breda Mod.39
40 mm	40 mm/39 Vickers-Terni mod.1915/1917 · 40 mm/39 Vickers-Terni mod.1915/1917, Modif.1930 · 40 mm/70 Breda-Bofors type 107
65 mm	65 mm/64 Ansaldo-Terni Mod.1939
76 mm	76 mm/40 Armstrong mod.1897/1910 · 76 mm/40 Armstrong mod.1897/1912 · 76 mm/40 Ansaldo mod.1917 · 76 mm/45 Schneider mod.1911 · 76 mm/50 Vickers mod.1909 · 76 mm/62 OTO-Melara Compact · 76-mm/62 SMP 3
90 mm	90 mm/50 Ansaldo model 1939
100 mm	100 mm/47 O.T.O. Mod. 1928 · 100 mm/47 O.T.O. Mod. 1937
120 mm	120 mm/45 Canet-Schneider-Armstrong mod.1918-19 · 120 mm/50 Armstrong model 1909 · 120 mm/45 O.T.O. Mod. 1926 · 120 mm/50 Ansaldo mod.1926 · 120 mm/50 O.T.O. Mod.1936
135 mm	135 mm/45 O.T.O. Mod. 1937
152 mm	152 mm/45 Schneider mod.1911 · 152/53 mm Ansaldo mod.1926 · 152/53 mm O.T.O. Mod.1929
203 mm	203 mm/50 Ansaldo mod.1924 · 203 mm/53 Ansaldo mod.1927
305 mm	305 mm/46 Armstrong model 1909 · 305 mm/46 Vickers model 1909
320 mm	320 mm/44 OTO model 1934 · 320 mm/44 Ansaldo model 1936
	Foreign:
20 mm	2 cm/65 Flakvierling 38 ^(Germany) · 20 mm/70 Oerlikon Mk.II ^(USA)
40 mm	Bofors L/60 Mark 1 ^(USA) · Bofors L/60 Mark 3 ^(USA)
76 mm	76 mm/50 Mk.33 ^(USA)
127 mm	127 mm/38 Mk.12 ^(USA)