M4A1 FRONT HULL ARMOR

[rexford]

Robert Livingston did some measurements on a real M4A1, and it is alot more vulnerable than other Shermans with 55°/56° glacis angles.

The center portion of the glacis has 51mm at 52°, 53° and 55°, and the large driver hood is 64mm at only 35°. In addition, M4A1 front hull armor is all cast, which could lower the 85% quality modifier even further (the 85% quality appears to apply to rolled armor with flaws, and cast is less resistant than rolled).

While 56° glacis Shermans with rolled and cast armor put extra plates over the driver and MG hoods to bolster very weak areas, it was not done on the M4A1.

As noted by Robert in his AFV NEWS report, M4A1's were viewed as so easy to penetrate that 743rd Bn tankers kept them out of combat.

M4A1's may have curved surfaces that will occasionally cause a bounce, but the weak areas are right in the middle and would seem to make the tank inferior to other Shermans.

[M Hofbauer]

the Master of LARGE CAPS THREAD TITLES strikes once again...

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"Im off to NZ police collage" (GAZ_NZ)

[Bullethead]

Rexford said:

<BLOCKQUOTE>quote:</font><HR>The center portion of the glacis has 51mm at 52°, 53° and 55°, and the large driver hood is 64mm at only 35°.<HR></BLOCKQUOTE>

This is what I was asking you in the Firefly II thread. The Brits called the M4A1 a Sherman II, but you said in that thread they had 47^ slopes. I'd never heard of such a thing on this model.

<BLOCKQUOTE>quote:</font><HR>In addition, M4A1 front hull armor is all cast, which could lower the 85% quality modifier even further (the 85% quality appears to apply to rolled armor with flaws, and cast is less resistant than rolled).<HR></BLOCKQUOTE>

I don't agree with this statement. There are many advantages to casting tank hulls and turrets compared to welding them up out of small plates. This is why, until modern composite armor was developed, most post-war tanks had predominantly cast components.

Some of the advantages of cast structures are as follows:

1. The force of an impact is more easily spread throughout the structure instead of being isolated in a small area by plate seams. This allows the armor to be harder than that made of small plates, leading to better resistance to penetration without excessive cracking when hit. Also, there is no chance of an impact breaking welded joints and dislodging an entire plate, even if it's not penetrated.

2. The curvature possible with cast surfaces not only increases the odds of a ricochet from an AP projectile, but also has a tendency to disrupt the proper formation of the jet from shaped charge warheads.

3. The metalurgical properties of the structure are more uniform throughout due to all being "cooked" at once in the same casting and heat treating processes. With welded structures, the welding itself changes the metal's properties in the area of the weld, usually making it softer and more easily penetrated.

All the above (except the part about shaped charges) were recognized well before WW2, in fact before even WW1. They were employed in battleship armor schemes that far back. The shaped charge bit was noticed during WW2.

Knowing these advantages was why the US built cast tank hulls. This was the preferred method, in fact, and was used on the M3A1 Medium and T1E2/M6 Heavy tanks as well as the M4A1. And at first, the only reason for having welded versions was because only a few manufacturers had the plant required to make such large castings. And when the 47^ slope came into production, the main reason there wasn't a cast version of it was wartime expediency. It takes far longer to "de-bug" a casting to eliminate voids than it does to simply weld something together. Also, it takes longer to make and properly cook a large casting than it does to make and weld together the smaller parts.

Note also that the front hull of the M26 Pershing was cast, at least the upper slope.

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-Bullethead

In wine there is wisdom, in beer there is strength, in water there is bacteria.

[This message has been edited by Bullethead (edited 01-08-2001).]

[Compassion]

cleanup bump

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punT!

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punT!

[hnh3_cm]

bump (if for no other reason than to annoy certain people )

[rexford]

Cast armor has less impact resistance because rolling change structure. Cast armor has less penetration resistance than rolled, cast 2" hit by 75mm has -14% less penetration resistance than 2" rolled.

Looking at the front hull of the M4A1, it has a large % of area that would deflect alot of hits due to vertical and lateral angles.

A smaller defeatable area may compensate to a degree for weaker armor. Good point about welded armor, although later 56° glacis Shermans may have had few glacis pieces.