Yes, there is overlap between ‘army’ and ‘navy’, as several people have pointed out. My idea is that between them, they cover all the critical elements of ‘military’, and that standing alone, they wouldn’t have done so. Because the navy is something ‘out there’, and the army is being restricted precisely because it isn’t ‘out there’. And the army is something you are calling up because you don’t want a standing army, but the navy is something you own because you do want a standing navy.
I think that capital and recurring costs are critical elements in constitutions in general, and that occupation and projection seem to have been important to the USA constitution, and that between them ‘army’ and ‘navy’ seem to make those critical elements clear in a way that merely ‘army’ or merely ‘navy’ would not have done.
I don’t have to think that ‘army’ and ‘navy’ are entirely different things to think that between them they solve the constitutional questions that I see. We could be arguing about if the government was constitutionally able to own tanks: clearly not thought of. We could be arguing about the navel militia: but we aren’t. Between them, ‘army’ and ‘navy’ as referenced in the constitution answer the arguments that matter - both then and now.
I’m not the supreme court, nor a historian, nor the common will of the people, this is just what it looks like to me, after trying to make constitutions work when I was younger, and I haven’t seen anything new here that makes me think that earth and air and water were something people cared about then or now.
I come from a political tradition that explicitly rejects ritualism, which I don’t deny, so I may be conscripting the originators into my own beliefs, but it seems to me that the originators also mostly were part of that same political tradition, and the constitution was and remains about real political questions like ‘how much power will the central government have, and in what (logical/political) areas’