Effectiveness of light aircraft cannons against ships

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Can't post an online source but it is on page 42, 1st paragraph right hand column of "Flying guns of World War II" by Anthony Williams and Emmanuel Gustin.

AS for the .50 working on those boats, I never said it wouldn't.

Only problem is that the planes listed in the 1st post of this thread were used by countries that did NOT use the .50 cal Browning. They didn't use the Hispano but the planes listed did use 15mm or 20mm cannon. The Question was if those guns would work against "ships".
Since "ships" covers just about everything from a 200 ton (or smaller) coaster to a 60,000 ton battleship it is rather obvious that the aircraft cannon don't work on everything.
Since "shipping" can also include wooden hulled coastal traders and fishing boats it should also be obvious that a single 20mm cannon may have some effect on them too. Or better effect than one or two 7.7-7.9mm machine guns.
 
But since the OP also mentioned the 37mm (COW) cannon that was to have been mounted on the Sunderland - it's fair to include that (it was used on earlier RAF Flying boats.
Granted the 37mm COW gun was used OTL in combat aircraft (apart from its developed 40mm S gun in the Hurricane tank-buster.

Its just that I had the thought of a earlier Wellington Torpedo armed aircraft, where the ground crew come across some apparently forgotten cannon and fit one in the bomb aimer's position - I wonder what reaction the shell's impacts will have!?
 
 
I don't know what kind of armor plate. Face hardened or what.

Did they ever try 30mm HE against the FV432?

Armor penetration or destruction is not always liner.

If a projectile/explosive charge can over match the plate it can often do quite a bit to it but hardly damage a slightly thicker plate.

For instance the Penetration of the old M1 ball .50 cal round at 200yds was supposed to go through 1/4in armor but against 3/8s it only penetrated 0.1 in. at 600yds against 1.4in in penetrated 0.2 in but against the 3/8s plate only .02 in.

If the armor they testing against was brittle (very hard) it might have cracked/broken instead of bending/denting.

Were the Rarden rounds detonating on the surface or busting a up to 50mm hole through the armor and detonating inside, which is what an APHE round is supposed to do.
 
Having spent some time at sea on some WWII vintage DD's and DE's, the numerous Fletcher class DD was provided along the middle portion of the hull in the way of machinery spaces with 20LB (0.5") STS plating, nominally proof against most strafing rounds. Such plating also was provided to portions of the bridge areas and M37 fire control director. Other splinter protection STS (Special Treatment Steel) was provided for various positions, probably along the lines of 10 lb or 1/4".

Even for a battleship the topsides environs of ship control positions and exposed AA crews could be quite threatened by strafing.
 
The RAF found that the AP rockets were extremely effective against ships, much preferring them to the 57mm Molins cannon. If an AP rocket hit the sea just short of the target the rockets would still keep on moving and would knock quite large holes in the hull causing flooding. If it hit the hull the rocket would penetrate and the rocket motor would almost certainly start a fire. It didn't matter if the target was a merchant ship or a destroyer, what mattered was if it had an armoured belt, which meant anything less than a cruiser was at risk.

The German 5.9in armed destroyer Z24 was twice attacked by rocket armed aircraft. both times she just made it back to base but on the second occasion capsized next to the quay.
A number of U boats were sunk with the rockets together with a lot of merchant shipping. Tragically of the D Days landings a number of British Fleet Minesweepers were sunk and damaged by Rocket armed Typhoons. I'm pretty sure they also sank one of Italy's largest liners but I cannot find the details right now and might be wrong.

0.5 in HMG and 20mm cannons would never do such damage.
 
I don't know about an Italian liner but they did sink the Cap Arcona in a rather tragic incident.

Accounts on the internet differ between one squadron and four, some accounts also mention bombs.

Very few people expect to sink large ships (large being from around 500 tons) an up with machine gun or automatic cannon fire. It has happened on very rare occasions, partially due to poor damage control and sometimes due to stored ordnance on the ship being attacked exploding (which certainly changes things).
But even 500 ton coastal freighters or fishing craft are large ones and there were many, many small coastal craft that could be sunk by aircraft guns.
With a fair number of the even small commercial boats in WW II powered by steam hits in the boiler or steam piping could kill the power leaving the craft helpless. A steam power plant being much larger in volume than a motor (diesel) power plant in such craft.
 
Shortround6 said:
I don't know what kind of armor plate. Face hardened or what.
Click to expand...

I have one listing of 9mm and a few listings of 8mm penetration vs. IT70 plate. 20mm Hispano-Suiza HE/I round, 200 yards, 0 degrees.

The '75mm to 200mm' hole is more like the damage expected vs. self-sealing tanks.

For what its worth the British ran a lot of tests on Hispano ammunition (air attack) vs. Uboat hulls and landing craft. Conclusions were that all types were ineffective at holing the hulls.
 
Don't know if 30mm fits into category of "light cannons" in this case. Just to share details of two maritime accidents involving 30mm cannons which ended in different ways.

1. Once I had an opportunity to inspect damages done to the tanker which was caught in a crossfire in the Gulf of Aden. Several shells (as I remember not more than 10) has hit the vessel's superstructure on the port side. Since the attacker was Soviet built missile boat (operated by one of conflicting Yemen factions), the weapon used was most probably AK-230 cannon. The picture was rather ugly: huge dents, many scratches, some cracks, broken railings. But no holes.
I don't remember what was the distance and angle of firing. Overall, the damages could be considered "cosmetic", yet should some rounds landed 15-20 metres aft and low they could destroy the emergency generator compartment (doors usually open in hot climate) and cause serious fire.

2. In 2009 cargo vessel New Star (DWT 5000 mt) was pursued and fired upon by Russian Coast Guard in the Sea of Japan. Patrol ship Primorye expended 515 shells before New Star changed her course back to Nakhodka (port of departure). She did not make it to the port and sank with a loss of 8 crew. Main weapon of Primorye was AK-230. No information about how many shells of total 515 has hit the vessel actually (there were some warning shots at the beginning). Damages below waterline were the most critical, the vessel listed starboard with forward trim when the crew began to leave her.
Сухогруз New Star расстреляли и потопили российские пограничники
 
In the Battle off Samar portion of the Battle of Leyte Gulf, the planes from the escort carriers carried something on the order of a half million rounds of .50 caliber ammunition to use against the attacking Japanese ships. They also had both the incentive and opportunity to use it all. (I don't have any figures on the actual number of rounds used.) Reports from the battle say that it was common for the planes to make repeated straffing runs until they exhausted ammunition. Despite all the strafing, I have found no indication that strafing caused any dehabilitating damage. (Similarly, not a lot of damages was attributed to 5-inch rockets carried by numerous planes.) Two heavy cruisers were sunk after their own torpedos exploded, but those explosions weren't traced to strafing attacks. In the case of the Suzuya it was a near miss from a bomb from a TBM, and in the case of the Chokai, it was attributed to a 5-inch shell from the White Plains.
 
The Japanese fleet off Samar under Kurita had a golden opportunity for their plan to work and disrupt the invasion fleet. Strafing may not have done much structural damage but can play considerable havoc with topside equipment and control positions. The most important issue is the Japanese turned away from the battle, the resistance put up by Taffy 3 and it's escorts in addition to the strafing was enough to save the day, much the effect of stumbling into a bees nest.
 
 

The ships that were straffed off Samar were carrying extra sailors who had been resucued from ships sunk in the previous days' sinkings by submaries and carrier aircraft. The chaos on those ships must have been unbelievable.
 
In prewar US destroyer development considerable controversy was developed over the pros and cons of light STS plating over machinery spaces. Pre war the destroyer tonnages were limited and it wasn't till the larger Fletchers that this could be easily accommodated. The main concern was the damage that penetration of machinery spaces and the vulnerability of very high temperature and pressure steam plants. An example of what can happen was the frequent steam explosions of strafed railroad locomotives.
 
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