Effectiveness of light aircraft cannons against ships

[Bob_Semple_Airplane]

Many Axis aircraft in WWII were fitted with light autocannon for anti-shipping operations: He 115 (15mm), Do 217 (15mm), Arado 196 (20mm), Aichi E13A (20mm), Aichi E16A (20mm). Also the Sunderland was originally intended to have a 37mm piece in the nose. To me, the idea that guns of this size could cause significant damage anything bigger than a corvette seems dubious. Does anyone have any information or combat accounts on the effectiveness of these weapons?

 

[davebender]

I think forward firing machineguns and light cannon are primarily for flak suppression.

 

[Shortround6]

Many Axis aircraft in WWII were fitted with light autocannon for anti-shipping operations: He 115 (15mm), Do 217 (15mm), Arado 196 (20mm), Aichi E13A (20mm), Aichi E16A (20mm). Also the Sunderland was originally intended to have a 37mm piece in the nose. To me, the idea that guns of this size could cause significant damage anything bigger than a corvette seems dubious. Does anyone have any information or combat accounts on the effectiveness of these weapons?

It is dubious. But there were an awful lot of ships (boats?) much smaller than corvettes. Fishing trawlers, coastal freighters, barges:

And some that were half her size.

In the Pacific you can count trading schooners, Junks and other small coastal craft.

 

[pinsog]

Straffing an empty ship is one thing, but if you are shooting at a fully loaded ship like a destroyer or light cruiser with even a 50 Browning and you hit either a torpedo or depth charge......BOOM!!
Ordnance on board a ship isn't always dangerous just to the enemy.

 

[Jenisch]

Hellcats having some fun:


View: https://www.youtube.com/watch?v=WhWelWiqfvI

 

[Ainene]

Straffing an empty ship is one thing, but if you are shooting at a fully loaded ship like a destroyer or light cruiser with even a 50 Browning and you hit either a torpedo or depth charge......BOOM!!
Ordnance on board a ship isn't always dangerous just to the enemy.

On destroyer-sized warships and larger ammo has splinter protection. Against mashine guns/light cannons it is enough. Against depth charges - probably, but can't remember certain cases(from bullet hits).
Against light cruiser - almost useless - much better to strafe bridge/AA batteries, to achieve certain result.

 

[tyrodtom]

The shipping some of these aircraft were intended to operate against was merchant shipping and submarines, not destroyers and up.
There's a quantum leap in the defensive capabilities between a merchant ship and a destroyer.

 

[Kryten]

Mossies and Beaufighters of coastal command used 20mm hispano to do considerable damage to light vessels not worthy of a rocket or bomb!

 

[Jenisch]

AP rockets would not be a better option to sink light vessels?

 

[dobbie]

I would think that 20MM and heavier would be very effective against smaller cargo vessels and such. Not so much against DE's on up because of their AA capabilities. Still, a long burst of 20MM or better against the bridge or gun directors could impede the ships capability. AT rockets would be even better. B25's with that 3 inch cannon were supposed to be effective against shipping too.

 

[Jenisch]

View attachment 229885

In a vessel such as this, AP rockets would easily perforate the hull, while hiting the cabin and perhaps destroying the controls. Maybe explosive rockets be a better option. But this only after the machine gun "inspection" constated that there was no explosive cargo onboard.

 

[davebender]

Unless hit below the waterline such small holes would probably cause only superficial damage to a ship larger then 500 tons in size. 1980s Persian Gulf tanker wars are a good example of this. Iranian speedboats peppered oil tankers with RPGs but most hits caused little damage.

 

[Glider]

The RAF strke wings used AP rockets against shipping. Those that fell slightly short were called wet hits as the rocket would continue underwater and knock a hole about 4ft square below the waterline. Those that hit the ship, (dry hits) would penetrate and the still burning rocket fuel would normally start fires.
The cannons were used to suppress the AA fire on the way in.

 

[Milosh]

On small warships like destroyers and smaller, the .50" could easily penetrate the hull causing internal damage.

 

[Shortround6]

Most of the planes mentioned were armed with those guns several years before rockets became common. Rockets would be more effective but if you don't have rockets?

Merchant ships also have fewer water tight compartments (one hole can flood more of the ship) and smaller crews ( fewer men on damage control parties) and perhaps less pumping capacity? warships are built with pumps expecting to take damage.
Merchant ships only expect to take damage in a collision or running aground (or leaking through decks in bad weather) NOT as part of their "normal" duties.

A single 15mm-20mm cannon shell MAY be able to make a hole 15-30cm across in the hull.

 

[Ainene]

A single 15mm-20mm cannon shell MAY be able to make a hole 15-30cm across in the hull.

Ship hulls(i mean notable warships) are made from quite thick high-tension steel.
So-only small hole, and very few energy even in case of penetration.
But yes, it's enough for smaller warships(i mentioned HMS Comus yearlier,though it was 23mm fire,not 0.50) to penetrate steam pipelines, for example.

 

[Shortround6]

Some ships (like some destroyers) were made of 3/8s (9.5mm) plating in may areas.

British 20mm Hispano MK 1.z HE shells were expected to blow a hole 75mm to 200mm in diameter in 12mm armor plate (type not given). Destroyers may use a grade of high tensile steel but it is not armor and some of the older coasters/fishing boats were made of sheet/plate iron, not steel, let alone high tensile steel.

The He 111s used a flexible mounted MG/FF with a 15 round drum not the 60 round drum used in the fighters. Trying to engage a destroyer with a single 20mm MG/FF and perhaps an additional MG 15 doesn't sound like the best tactics.

Engaging merchant ships that might have a Lewis gun or two (if they are lucky) sounds like a better bet.

 

[davebender]

He-111s also carried bombs (for skip bombing) or two torpedos. After getting hit with a torpedo I doubt anyone cared about the tiny amount of damage caused by cannon fire.

 

[Ainene]

Some ships (like some destroyers) were made of 3/8s (9.5mm) plating in may areas.

British 20mm Hispano MK 1.z HE shells were expected to blow a hole 75mm to 200mm in diameter in 12mm armor plate (type not given). Destroyers may use a grade of high tensile steel but it is not armor and some of the older coasters/fishing boats were made of sheet/plate iron, not steel, let alone high tensile steel.

It's HE shell,completely different case.
Also, if possible, can you post some links about expected Hispano HE damage? Damage you listed looks too high, from my perspective.
p.s. coasters/fishing boats, and smaller escort(or coastal) combatants out of question - .50 was used in this role everywhere with success.

 

[CobberKane]

I would have thought that the anti-personnel properties of six .50s or four 20mms directed against an unarmoured merchant ship, even on of considerable size, would have been significant. I have read an account of a F6F pilot who strafed a Japanese cruiser and spoke of 'bodies everywhere'.