We are currently being instructed on how to lock up our new building.  In order to set the ”crash bar” in the locked position, we must use an Allen Wrench to ”dog down” the door using a “dog key” which is the Allen Wrench by another name.

What do dogs have to do with any of this?

Probably the same as dog down the hatches.

Edit: I speculate that the use of “dog” for a device used for holding or gripping something developed from the image a dog biting and holding something.  Bulldogs and fighting dogs are particularly notable for getting something in their jaws and not letting go, but you can see the same behavior in most almost any pooch if you play tug-of-war with it, using a towel or one of those dog toys made just for that purpose. Maybe retrievers are more willing to let go, but most dogs are pretty stubborn about it in my experience.

Many thanks, Dr. T!

Makes good sense.

"Cry havoc, and let slip the dogs of war...” On first thought, the Bard seems to refer to fierce, warlike canines being let off their leashes.  But what if war is conceived as a kind of whirling maelstrom confined within a vessel, the vessel having a lid held down by movable latches ("dogs")—so that when the dogs are slipped, the maelstrom will burst forth violently.  I like the image, but perhaps this is too far-fetched??

Yes.

The ancients did use dogs in warfare, to attack the enemy.  See the Wikipedia article on Dogs in warfare.