In this context, he was talking about carbon fibre, not aluminium (though, aluminium would also be a less than ideal material to make a deep-water submersible out of).

this wasn't an aircraft

The reference to "aircraft" wasn't about airplanes or submersibles, it was about how the term "aircraft-grade" is a meaningless marketing buzzword. It's obvious to me, and I imagine a lot of readers, that a submarine isn't an aircraft. I think the reference to the use of the bullshit marketing term is also obvious.

"Military grade" is another one of those marketing phrases that pisses me off. What does it even mean? That it is green and is more expensive than it should be?

Occasionally, they will identify a particular MIL-STD (or MIL-SPEC) that the product supposedly complies with; whether or not there is any substance to this claim and whether or not, if you looked up the standard, it would have any bearing on suitability for the purpose the product is marketed for is a mixed bag.

I think I read a comment on HN that described what "military grade" meant: stuff made as cheaply as possible by the lowest bidding contractor that sometimes is fit for purpose.

That said, I think there are times when it does mean something. I believe military grade/milspec chips/ICs are often engineered to be more resilient to environmental factors like heat and vibration, interference, etc. If I'm wrong about that, I suspect it won't be long before we learn if I'm right.

There are some compabies that actually do test theor products according to military standards. Now, ideally they would tell you which ones. Whether or not those standards are better than theor civilain counterparts is a different story.

In my (very short, many years ago) stint as an EE it meant that parts (transistors, ICs, etc.) were guaranteed to work within certain specs within certain operating conditions (temp, etc.).

It did not guarantee anything outside of that. Soundness of design and ensuring inputs and environmental factors conformed to the spec was up to the engineers.

Military grade does not mean it is any better built than anything else. it does however mean it is often better specified. So it does not mean anything in regards to suitability to purpose it does mean there is a document that describes the product and the product meats the requirements of the document. Which can be nice if your requirements are also matched by the document.

The problem, it is a military specification so the public may not be able get access to it.

No, but the point is that in such a scenario, the material deficiencies and failure modes are mostly pretty well understood.

> It means you're using a material that's been vetted over decades in life-critical applications in harsh conditions by expert engineers all over the world.

If I start using a screwdriver to hammer in nails, it doesn't matter how many expert engineers use screwdrivers. I'm using it for a purpose it is unfit for.

Just because it's aircraft grade doesn't mean that it is (or isn't) suitable for building a submarine.