This is a very interesting topic to me, and I'm going to try and refine some of my points in light of everyone's posts thus far. Please don't take these responses as combative. I'll simply be trying to provide contrast and expand the discussion. tl;dr at the bottom of the post
on Oceanic planets you'd most certainly need wet navies...makeshift and multi-use craft likely couldn't match the "home advantage" dedicated craft would have.
Would not a dedicated surface vessel be inferior to a weapons platform that could travel and fight above, on, and below the liquid surface? It would be like the
Hindenburg trying to fight an
Apache.
this would depend from world to world, no need for a navy on a world with no bodies of open water.
I believe this
reinforces the strategic advantage of developing and fielding one all-environment or multi-use vehicle instead of multiple environment-specific ones. Orbit-bound fleets need only bring along one division of ground forces equipped with such versatile vehicles rather than separate divisions of land, sea, and air forces.
Moreover, specialized equipment requires a multiplication of training and support apparatuses whereas a unified platform and force only needs one pipeline for men and materiel. It would be much easier to pick up a regiment of troops trained on a wet planet and deploy them to an arid one if the equipment they use remains essentially the same.
A space-bound weapon is a blunt instrument. Any weapon system that can be de-orbited or fired directly to the surface, is large and fast enough to penetrate anti-ballistic defense systems on the surface, and hit a target, will probably also crater most of the surrounding area, if only from the kinetic energy involved.
Strategic bombardment needn't necessarily be
kinetic bombardment. You could perhaps penetrate defense systems by saturating them with comparatively low-velocity munitions rather than one non-interceptable high-velocity attack or render defenses useless by entirely non-kinetic means (electronic warfare, EMP, sabotage). There would certainly be other tools available to achieve the same effect, if desired.
let's look at Afghanistan and the U.S. operations there
Thank you for sharing this, Saxon. The stealth bomber pilot's story is an excellent illustration of the need for boots on the ground in certain situations. You cannot win hearts and minds with giant bombs.
Orbital bombardment is a good way to start, but unless you're going for a scorched earth policy, you'll need conventional troops to finish the job.
I agree completely, but I think I define "conventional troops" in this respect differently that most of you might.
The stealth bomber, with pinpoint guidance from special operations assets, took out all conventional resistance and then some just to be sure. In sci-fi terms, it functions as the dominant fleet in orbit over a target planet, reducing the enemy's ground defenses before a landing.
Now, the main body of troops arriving after such bombardment is there for, as Julianus says, the "acquisition of supplies, labor, factories, and sensitive intelligence" and more directly the acquisition of "[p]opulations, infrastructure, industry, culture". Those things are the real prize. Yet, counterintuitively, they
are not won with tanks and guns.
The true battle in post-invasion Iraq and post-bombardment Afghanistan is/was fought on "human terrain". The primary forces in such a fight consist of civil affairs, civil engineering, intelligence, and psychological operations forces. If you can get them to like you enough and cow the loudest of them that resists, guerrilla attack will subside, the people will cooperate with you, and they'll adopt the cultural traits you want them to have.
Unfortunately...
a dude with a gun and some basic comm gear, body armor, and perhaps an APC
...cannot win that fight.
Here's the chron that I think applies most directly to this topic.
The kernel of victory in a war fought on "human terrain" would look like this, a line from that chron, taking place in the narrative of the target population:
In a whisper Jeb asked me whether we were lost, and I didn't know what to tell him. A part of me - the rebellious part, I supposed, though it didn't feel quite so - wanted to say yes. Another, more sensible part suspected that we might have a new world on our hands.
"We might have a new world on our hands." Tacit realization that perhaps invasion wasn't the end of everything good. There might be hope or even benefit in adapting and changing to fit in with the invaders. You get them all (or enough) to think like that, and you create a new subject and/or allied nation out of an enemy.
tl;dr What you need are big guns up top and dropships full of Quafe and exotic dancers.