It's important for any organisation to understand the business it's really in. Take Coca Cola as an example. You can be anywhere in the world and buy a Coke out of a fridge with the Coke logo on it. They happen to sell fizzy drinks, but their actual business is in branding and logistics. You could give those guys any product and they could shift it in the same way. Or you could say the same for Starbucks, they don't compete on making better coffee than their competition! Your HR company probably doesn't really do HR as such, it probably does operations and the COO will be the logical choice for CEO.
The Army doesn't really understand this about itself because it's a brave officer indeed who's the one to say "actually, we need the RLC much, much more than we need the Paras or the Guards"...