"Depth Charging Tanks?" Topic

I wasn't sure whether to put this in the WWII Land or Sea board :)

I was just reading in Samuel Eliot Morison's "Operations in North African Waters" that American carrier aircraft dropped 325-lb and 100-lb depth charges with contact fuses on French tanks during the Torch operation. He writes:

"The effect of a depth charge on a tank was devastating. It did not destroy the shell, but reduced the interior and all its contents to scrap and powder."

Yikes!

If I remember correctly the Luftwaffe dropped mines on land targets in the UK during bombing raids as well.

Sounds also like a weapon of choice against the diving snorkel tanks that Germans were preparing for the Operation Sea Lion.

In this context how is a depth charge different from a bomb?

Probably not much difference from the point of view of the targets.

A depth charge sinks much faster in air than in water.
A bomb would fall at the same rate in either medium.

No, physics wasn't my strong suit.

Aerial Mines were almost pure explosive in a very thin casing. Bombs came with a very strong outer shell.

Why? Because bombs dropped at a rate determined by Newton and their landing site could be reasonably predicted. The snag is they had to survive contact with the ground to then operate and make a loud bang. Hence the stout casing, at the expense of the HE content

Ah. A mine must be dropped by parachute or it will never survive landing. The advantage…..a very big bang indeed for its size. The snag? Where will it land? So only used for city bombing where accuracy not an issue.

A depth charge will be influenced solely by gravity, not its mass. Cannonball and musketball off the Leaning Tower thing. In any medium both a bomb and depth charge will accelerate under gravity at the same rate….except a bomb has probably already reached its terminal velocity in air and a depth charge probably started out just above the surface of the water (and its larger surface area does create some drag, for that reason the musketball probably hit an instant before the much more massive cannonball))

Yeah hitting an AFV on the top deck with something that big from the air even if it didn't explode would some damage. Especially on the early war tanks like the French were using at that time. Or pretty much any AFV for that matter.

As deadhead pointed out it is gravity, i.e. something heavy falling from the sky on a target.

Reading further, they also used them with some effect against the French shore batteries--which had proved pretty impervious to naval gunfire.

The reference to the 325lb depth charge was almost certainly the USN Mk XVII. This was a 325lb aerial depth charge carrying 234lbs of explosives (don't know what type, although Torpex and TNT were common HE fillers in USN depth charges). According to Paul Silverstone (The Navy of World War II, 1922-1947), this was the USN's ONLY purpose-designed aerial depth charge in WW2. Any other depth charge dropped by air would have been an improvisation. But it appears improvised aerial depth charges were not uncommon.

The only reference I can find to a 100lb USN depth charge would be the Mk 1 (no relation), which was 100lb and carried 50lbs of explosives (Gun Cotton). This was a 1916 design. USN research had shown that larger HE charges were more effective, even if it meant fewer charges could be carried or dropped, so all subsequent designs were notably larger (except the 22lb Mk 10, which was intended for use close aboard ship hulls against frogmen and midget submarines).

I have not found any specific information yet about the HE content of USN aerial bombs, but from prior readings about air force bombs a GP bomb of 500lb weight might be expected to have something like 80 – 120lbs of HE filler.

I can easily see an environment were USN ships crossed the Atlantic with substantial load-outs of aerial depth charges, to ensure active defense against U-Boats. But once they reached the coast of French North Africa, German U-Boats would be of less concern than French naval surface combatants. So SAP and GP aerial bombs migh be held in reserve while some of the aerial depth charges, and the old "surplus" light depth charges with some improvised fins added, might be dropped on ground targets.

But that is all my supposition, with little detailed documented support.

I also strongly expect that the accounts of leaving the shells of tanks that were hit intact, but scrambling the insides was not a reference to direct hits. If it detonated, a 234lb HE charge on the top of an R35 or D1 tank would probably have resulted in scrap metal distributed over a wide area, with MAYBE a little bit of what could be identified as "oh this might have been a tank". But then, the probabilities of hitting a tank sized target with an aerial bomb would have been perhaps 100-to-1. So I doubt any number of hits were scored.

But having 234lbs of HE go off within a few yards of an R35 or D1 tank would probably have put that tank in a very bad way, and put any crew inside it into another state of being vs. what they were (ie: alive, conscious, functioning) before the event.

Just my guesses.

-Mark
(aka: Mk 1. Not a 1916 depth charge, although I can do a pretty mean cannonball from a low diving board with any spring to it.)

I have not found any specific information yet about the HE content of USN aerial bombs, but from prior readings about air force bombs a GP bomb of 500lb weight might be expected to have something like 80 – 120lbs of HE filler.

Eeyup!

One of those Mk17 Depth Charges has the explosive weight of a 750lb bomb, which will ruin anyone's day.

Yeah even a near miss depending on the size would do some damage, as I said especially to the early French and others' AFVs. Again even if the "bomb" didn't detonate it could do some damage. Even if the AFVs was not that damaged, the crew may not have been so lucky …

A depth charge will be influenced solely by gravity, not its mass.

true, if dropped in a vacuum.

The accounts I've read indicated it was CL Savannah's OS2U scout planes that used depth charges, fuses set to explode on impact, against both the french tank column destroying 3 tanks and silencing the shore batteries firing at DD Dallas.

Another use of the depth charge on land, the Australian Matilda II Hedgehog tank was designed to fire depth charges off its rear deck for the purpose of devastating the interiors of Japanese bunkers and cave systems.

As long as it works …

Mass and gravity and medium it passes through. Totally true as I said end of paragraph…..the bit about the musket ball probably hit the ground before the cannonball. We have all seen the Apollo film, of a feather and a mallet, which was of course purely fake news we are now told (God help us all)

I had not thought that an aerial-dropped explosive with a contact fuse was a "depth charge". They are totally different things. Now I can see how it could be done against land targets (less sure about why though)!

Each has its own advantage in ASW. A true depth charge is dropped from on high and will go bang at a certain pre set depth. Anyone nearby will have a thoroughly bad day . It just needs to be reasonably close to target. Good weapon even if it misses. On land it will surely shatter, without detonating?

A gadget with a contact fuse (like fired from a Hedgehog mortar) will only go bang on contact…but if it does so, you will not have even an instant moment to reflect on the right wing politics or racial views that sent you there. You will meet your maker and explain your political views rather quickly.

I could see a contact fuse ASW weapon dropped on tanks, but NO WAY a "Depth charge" (This from a Napoleonic Wars enthusiast who was just passing through however. Profound ignorance has never stopped me speaking with great authority on any subject)

In one of the Sven Hassel novels (I know, I know) he describes a UXB team having to defuse an aerial torpedo dropped in a bombing raid.

I'd have thought that made no sense at all. For its weight, an expensive torpedo surely contained less bang than a bomb because some of its weight was fuel, motor and guidance. But: were obsolete weapons ever "unloaded downrange via the barrel" in this way, as it were? If in 1943 you had a stash of obsolete WW1 14" torpedoes, you could either blow them up somewhere at sea, or drop them on Germany – so did this ever happen?

They could not survive the impact. Indeed aerial torpedoes would break up on the surface of the sea if dropped from any significant height.

Translation sometimes gets this wrong. Mortar rounds or Napoleonic shells become grenades for example

Mind you, what about a Kate dropping a naval shell onto a US Battleship? Of course that was AP with far less bang for its mass/weight, but if it could and indeed did penetrate to a magazine and……….

Each has its own advantage in ASW. A true depth charge is dropped from on high and will go bang at a certain pre set depth. Anyone nearby will have a thoroughly bad day . It just needs to be reasonably close to target. Good weapon even if it misses. On land it will surely shatter, without detonating?

If you could set the WW2 depth charges to detonate on impact with the water, instead of after reaching a specific depth, they'd detonate on impact with ground, too.

Hitting water at high speed is like hitting concrete!