1953 76mm American projectile, what's with the round nosed base?

[Kilroy]

I've not seen too many like this, I was told that it was the true type of projectile used in the ammunition for the
first integrated AAA unit in the US Army or USAF, the aptly named "Skysweeper". The weapon consisted of an on-board radar
integrated with an early computer for fire control, and the capability of being large enough of a projectile at 76mm to
accept the VT fuses that were coming out by the 50's. Guided missiles came online shortly after and these units were quickly
passed from the scene although I read a few units might have made it to Korea and a few early AAA sites around US metropolitan areas.

Does this projectile look like that could be the correct type? I know data on this whole unit is sketchy, that is why
I am bringing it here. What was the reason for the hemispherical base? A new forging technology or was it better somehow?

I have attached a picture of the box top of the model kit, which was popular in it's time.

There is one complete Skysweeper for sale over here for anyone nostalgic for the Cold War.

Walt

 

[highlandotter]

I saw the Skyscapers installed in the early 1950s at the locks in Sault St. Marie, Michigan,. Soon after, the Nike sites seem to have displaced the AA guns.

 

[HAZORD]

Yes, the projectile you show is a 75mm Skysweeper projectile. When they designed it, they necked down a 76mm M26 case from the Super Sherman to 75mm.

There is a discussion of this projo and hemispherical bases in this post:

http://www.bocn.co.uk/vbforum/threads/41836-37-X-219SR-T68-Vigilante?highlight=skysweeper

The rounds were typically fuzed with proximity fuzes for antiaircraft work, but they could be used for direct fire against ground targets.

 

[hicky1300]

As I have always understood it the round base is derived from the german WWII Minegeschoss rounds.
The idea being that the round base gives a larger surface area for the propelling forces to act upon.
Obviously a concave base would do the same but reduce the internal volume, thereby less bang!
The convex base presents a larger surface area & increases the internal volume.
I think it also adds to the aerodynamics as a concave base would create a vacuum behind it whilst the projectile was in transit.

 

[Kilroy]

Re: 1953 75mm American projectile for Skysweeper AAA

Thanks for the confirmation. I have it mounted in what I **THINK** is the right case, it is so damn easy to get these things wrong.
Even Ian Hogg was sketchy on the particulars of this one because a number of units were built, the project closed, it was gone.
It was about 70% an R&D project anyway, but for it's time it was very advanced in it's amalgam of technologies to get a shell close to a plane.

OK, so now the projectile has a positive ID, here are a few additional pictures of the stamps on the projectile and the headstamp
and see if these are authentic.

Yes, the projectile you show is a 75mm Skysweeper projectile. When they designed it, they necked down a 76mm M26 case from the Super Sherman to 75mm.

 

[HAZORD]

That's probably the best looking Skysweeper case that I've ever seen.

 

[2pounder]

hemispherical bases have the same force propelling it up the barrel as any other shape. Rawlinson mentions this shape as being ideal in his book 'Defence of London 1915-1918'.

 

[Kilroy]

Yes, here in New Jersey where Nike/Ajax were deployed by sometime in the 50's at many locations, a 75mm gun was really not the answer to almost anything. Russian planes would be flying too high, missiles would also exceed the performance capabilities of that size gun in most situations except for sheer luck that something had come in so close they could get off some shots.

I have come to see it as a good first generation R&D project for anti-aircraft applications where it could still be a good and new answer to enemy planes and maybe even slow V2 type missiles in conventional combat situations, like Korea for instance. The days of a man trained in as a gunner on a 20mm Oerlikon was over due to the speed of the jets now flying in the air, handing the mission over to a computer and radar was a very good hybrid development, particularly withthe VT fuse to make that last judgement call!

I saw the Skyscapers installed in the early 1950s at the locks in Sault St. Marie, Michigan,. Soon after, the Nike sites seem to have displaced the AA guns.

 

[Kilroy]

Wow, thank you very much! You can definitely call that the correct case with the correct projectile? I was hoping for that, but it's hard to be sure.

The case is from a collector in upstate New York, I have negotiated privately with him for several rare items, but I do not think he knew this was
what it was, I think he thought it was just the Sherman Tank "long" case that came later. I don't recall what the correct name for them was.

The lacquer did indeed strike me as particularly well preserved, and I do not think there is much restoration of lacquer and other forms of
anti-oxidation coatings for steel. It was saved in a good place and left there undisturbed. The projectile fit into it snugly,
but not so tight as to need a press fit, I think it might be an unfired case.

Unfortunately, even if both pieces are authentic, the VT fuze will just be utterly impossible to obtain, at any price :bigsmile:

Thanks for the opinion, it's very encouraging!

Walt

That's probably the best looking Skysweeper case that I've ever seen.