It's not so much that it's military equipment. Some of it is just amazing engineering, regardless of context. Since many HNers are engineers, it is not surprising that posts about interesting/amazing feats of engineering get voted up.

One of my favourites (ignore the patriotic stuff in the beginning): http://www.wvi.com/~sr71webmaster/press_suit001.html

I wouldn't call the fastest airplane ever built to be just "military equipment". It's probably one of the greatest engineering achievements ever and it's still unsurpassed.

It's also a beautiful machine.

Didn't realise it was the fastest airplane ever built, that sheds some light on it. It is really a greater engineering feat than anything in the space program?

It depends on if you count the X-15 or the Shuttle, but neither of those were air-breathing.

The shuttle should be considered a glider (a lousy one) when landing. The X-15 is a rocket with wings and should be called a spaceplane - it crossed the 100 Km border twice after all, and couldn't take off by itself.

Agreed. The X-15 even had a RCS for when control surfaces no longer had enough air to bite into.

The coolest thing is the analog computer that seamlessly went between control surfaces and RCS as if it were flying using surfaces within an atmosphere. It may not be a "real" plane, but that doesn't make it any less amazing.

I'd love to see the X-15 progress into the X-20 and onwards.

I think the SR-71 interests most people despite being military equipment. It interests me in the same way that the X-15, Apollo, or SpaceX's Grasshopper interest me.

The SR-71 is a major milestone in human engineering that hasn't been matched in 4 decades. It's like we landed on the moon and stopped all progress. The plane carries no weapons and it's only purpose was to take pictures.

Nitpick, the SR-72, which this article is about, apparently would carry weapons.

People's interest is roughly proportional to the energy level involved. Energy is proportional to v^2, so fast things are extraordinarily interesting.