I have several UI Images positioned around a Scene that act as buttons.
Selecting an image sets a corresponding 3D object to active.
All the 3D Objects are closer to the Camera than the Images.
However when the 3D Objects become visible they are always behind the Images.
I have my Canvas set to World Space
ui is counted as GUI, it would be pretty stupid if your inventory would appear behind a tree, instead use a plane and use a material on the plane of your UI, then put the plane behind whatever it has to go behind
Answering my own question:
The reason the UI elements were showing up in front of the 3D Objects was because of the position of the Canvas, not the elements within the Canvas. I moved the Canvas behind the elements and it worked as expected.