Invading a planet from space is, to say the very least, problematic. Although many planets are given populations of perhaps a million or so inhabitants, I would imagine that strategically important locations could have populations of up to several billion.

During WW II, the United States was able to field a total military strength amounting to approximately 10% of its population. A planet with a billion inhabitants might be able to field a military strength of perhaps 100 million.

Additionally, a planet, while impossible to hide (at least with typical 23d and 24th century technology), would usually have a clear view of the surrounding space. Lacking superior stealth capability (as with the 23d century [TOS] Federation), an approaching force could be spotted by sensor outposts well in advance of arrival. A defending force of ships could easily be hidden in an asteroid field or on small moons within the system, and could perform hit-and-run attacks against an invading force. If sufficiently strong, a defending force could go head-to-head against an invader, reducing its strength prior to a ground assault. Surface installations and orbital defensive stations would further reduce an attacking force's strength.

Once in orbit, however, it seems an attacking force would have the advantage over surface-based defenses. They could use a wide variety of sensors to detect and target important ground-based installations. If the sole purpose of the invasion was to destroy the population of the planet, they could simply incinerate the surface with phaser fire and torpedoes.

If the objective is to occupy the planet and subdue the populace, however, the task is not so simple. If you sit up in orbit and simply blast any military formation you spot, you would still destroy significant amounts of the planet's eco-system. You could never be certain you had gotten all the combatants, and you'd still be stuck in orbit, without secure locations to send your forces to sieze control of the planet's infrastructure and resources.

Despite the advances in technology, even in the 23d and 24th century, you still need ground forces. My question is, what form do these forces take?

In our own time, a proper military force requires the following elements (and perhaps some more I've overlooked):

1. Infantry, the only type of force that can indisputably take control of and hold territory,

2. Artillery, which can provide massed firepower in large sustainable amounts,

3. Armor, which provides a great deal of mobile firepower, yet remains vulnerable to infantry in close quarters,

4. Counter-armor forces, including "tank killer" ground vehicles and specialized anti-tank aircraft,

5. Intelligence-gathering capability, provided by aircraft, sattellites, and remotely-piloted vehicles,

6. Air Forces, which provide long-ranged precision striking capability, allowing one to attack an enemy's infrastructure and troops massing in the rear for an attack,

7. Support elements, such as supply, messing facilities, and medical support.

Let's discuss how each of these elements is implemented in the 23d and 24th century world as shown in Trek. Where an element's form has been superceded by technological advances, the function will very likely still remain, but will simply take a new form (example: horse cavalry has been superceded by tanks, helicopters, and mobile infantry).

--Baloo

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"The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts."
--Bertrand Russell (1872-1970)
Come Hither and Yawn...

A 24th century Earth would probably import the majority of its food, such a world would probably surrender if cut off from resupply, rather then let a huge amount of its population die of starvation.

As I recall Betazed seemed to either surrender or fell extremely quickly during the Dominion war.

Another point is that even currently, the US military is developing a technology that can destroy a flying air-to-air style missile with a laser mounted on a 747 style plane.
In Star Trek, ships are fighting with phasers and other weapons at speeds probably at least half the speed of light(estimate). They can also hit targets with photon torpedos at FTL speeds. You realise that "small" miss at FTL speeds would mean a miss of hundreds if not thousands of kilometres. I think its a safe bet that a ship in orbit could easily destroy a 20km/h tank without even singing the grass underneath it.

So in the list:
1. Infantry: Obviously, we've seen infantry with "standard" uniforms, not very probable, but maybe phaser-style weapons are so powerful any armour would be useless unless they are on a Borg personal shield level?
2. Artillery: Easy target for starships, or even shuttles. Wouldn't it be easier just to "beam" a shell on top of the enemy instead of beaming down a gun to do the same thing?
3. Armour: Big f*ing target. Not likely
4. Anti-tank weapons: No Tanks....why anti-tank weapons?
5. Intellegence: Always useful, no argument
6. Air forces: Only useful for knocking down shuttles and other space to ground transports. Airfields are obvious targets so airplanes would have to be VTOL capable or something similar.

Major point:
ICBMs and battlefield nuclear weapons would be a large threat. They are capable of wiping out expensive armies in one blow if they don't have something that can knock them down mid-flight.

All in all, I think that warfare from space to the ground would be a moot point in most cases. Space superiority grants air superiority, air superiority grants victory in the oceans, a ground defending force could only hope to fight a holding action until reinforcements arrive in space.

I think Starfleet probably has some sort of ground assault vehicles that we have not seen in use by, what I will call, their Marine Corps. We've heard of "hoppers" which I took to be some kind of troop transport ship like the ones seen in "Starship Troopers".

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"A gathering of Angels appeared above my head. They sang to me this song of hope, and this is what they said..." -Styx

Aban's Illustration www.thespeakeasy.com/alanfore

If the above is not the case, then how could there be any surface combat at all?

Science officer (SO): "Captain! There seems to be an enemy formation approaching our surface deployment!"

Captain (C): "On screen! Magnify."

SO: "It appears to be a mix of personnel carriers and heavy support vehicles."

C: "How soon before they can threaten our units?"

SO: "One minute, thirty-two seconds!"

C: "Communications! Alert our units to the incoming threat."

Communications officer (CO): "Aye, sir!"

C: "Lock phasers on the lead elements."

Weapons Officer (WO): "Phasers locked! Ready to fire!"

CO: "Captain! Unable to raise the surface commander! They're using subspace interference generators!"

C: "Damn! Fire phasers!"

WO: "Phasers fired, sir!"

C: "Damage assessment?"

SO: "Four heavies destroyed. They are dispersing, but not retreating."

C: "Fire again!"

SO: "We can't establish a lock sir. They're emitting jammus particles."

C: "Compensate!"

SO: "I'm trying sir! They're oscillating the freem wavelengths and rotating the belzanwissels!"

C: "Can we risk a torpedo?"

SO: "They're too close to our units now. We'd damage our own as much as them."

Doesn't that sound plausible? If the defending forces have no reconnaissance capability other than the orbiting vessel, they're screwed.

Now we've had an example, I ask again: Just how are the units equipped? Speculate. Remember: just because you brought the biggest gun to the party doesn't mean you win the door prize. If you can't win except by destroying what you came to possess, why bother?

--Baloo

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"The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts."
--Bertrand Russell (1872-1970)
Come Hither and Yawn...

Here's another question, though. Ship enters orbit to deploy troops. Why can't the planet have surface to orbit weapons, to combat the ship? Planetary assault is more complicated that we make it out to be.

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"I see you have the ring. And that your Schwartz is as big as mine!
-Dark Helmet, Spaceballs

As for personal forcefields I really doubt they would be use in any large significant numbers. In the first episode the Borg showed up (Q Who?...can't remember) the appearance of personal shields was a major surprise...if Starfleet has access to them why would they be such a surprise that the Borg whould have them?

I think that you've overlooked something, surface combat seems to be almost an afterthought in Star Trek, standard uniformed ensigns battling it out with no armour.

Maybe there's a reason.....maybe combat "IS" an afterthought, one last way to thumb your nose at an opponent but rarely a deciding factor.
(Unless major castmemebers are involved, but thats another matter)

And as for jamming an opponent and getting close enough to friendly units that orbital fire cannot be used. I ask again, why land and risk units?

As for planetary assault, when's the last time a battle has been won with fortifications? The Maginot Line, D-Day, Sicily, Berlin, oh wait....those were losses. Just like Star Trek in Betazed, DS9 (In The Way of the Warrior) if reinforcements had not arrived), SOA, etc. I don't think static defences would be of much use when an attacking unit can use FTL tactics.

In this game we get to see designs for Romulan , Klingon and Fed ground vehicles , the game also highlights the tactics these three powers use , for example the Klingons send a Squadron of Bird's of Prey to provide cover while a division of tanks and troops land on the planet.

Theres a huge number of screencaps at : http://www.interplay.com/stnewworlds/media.html

These caps do give a nice peek into what a planetary attack might look like.

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"Marge .. Do you have other men in this House ? .. Radioactive men?"
~Homer "The Simpsons"

Jupiter Station , Starfleet Research & Development

First of all, I don't imagine that there is much in the way of heavy armor in Starfleet, for the following reasons. One, we know that a starship can hit ground targets with a large amount of accuracy and little if any damage to the surroundings. Kirk, for instance, would routinely call down phaser strikes on targets that he wasn't fifty feet away from. So I don't think that starships have to worry too much about hitting their own troops, save for the occasional melee. However, for that reason, it seems unlikely that troops would be kept very close together at all. 24th century technology would allow them to maintain unit cohesion at great distances. Hence, making it hard for a starship to effectively take out entire groups of soldiers at once. But armor, being larger, makes for a much more attractive target.

Voice of James Earl Jones: "We are the [insert name of invading people here]! We have destroyed your satellite system and over one hundred ships are poised to crush any resistance! Surrender and we will be merciful! Resist and be destroyed!"

As the last syllable of that message fades into the ether, sixty ships of the invading fleet are vaporized by lances of energy originating from the surface.

Voice of Don Knotts: "Oh yeah? You and what army? If you want this planet so bad, then come and get us!"

Now what does the commander of that particular fleet do if his mission is to enslave the population and capture the resources and infrastructure of the planet in as close to serviceable condition as possible? Does he just blow it to kingdom come as a warning to others? Does he turn around and go home? What if there's another fleet coming to the rescue? How long can they maintain their blockade? How can he be sure he knows the location of all surface batteries and destroy them should they open fire?

The reason you need to land troops is to ensure that you actually control the area you plan to occupy. I'd imagine it isn't always possible to destroy a surface installation from orbit, at least, not with a single shot. After all, you can have HUGE shield generators and power supplies on a planet. You could have multiple installations, all unmanned, which are intended to fire just a few times before the orbiting vessels can generate effective counterbattery fire. You KNOW it's hard to hide an orbiting ship. How difficult is it to conceal a phaser battery or photon torpedo launch facility when you have an entire world to hide it on? How difficult is it to create a decoy installation that is the 23d/24th century equivalent of artfully painted wood and canvas?

Keep tearing at it folks. We really don't know anything except that almost anything is possible. Anything except that surface combat is obsolete. It's difficult as hell, but it's never been an easy task, and probably never will be.

--Baloo

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"The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts."
--Bertrand Russell (1872-1970)
Come Hither and Yawn...

And here are all the thumbnails:
http://www.interplay.com/stnewworlds/media.html#ss

I beleive project "Thor" considered this use, with merely crowbar-sized projectiles. Fairly small mass + Lots of KI = lots of damage, with no attendant radioactivity.

Of course, the elephant-aliens in Footfall also dropped a good-sized meteor or comet in the Indian Ocean, the effects of which were global and wiped out a lot of potential defenders.

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Calvin: "No efficiency, no accountability... I tell you, Hobbes, it's a lousy way to run a Universe." -- Bill Watterson