Land, Air and.....hmm. Something is missing.

[Katharon]

Orbital ships pretty much make the use of surface ships invalid by default. There's a reason why those Armageddon orks built submarines and not surface ships.

[Stephen James Hand]

The last cavalry charge was during the Siege of Warsaw in 1939. It went better than you'd think, but ultimately still failed. Military commanders are also acutely aware that sometimes the old school is the best school. Take Operation Barbarossa. The German Panzers tear their way through Russia until they're in sight of Moscow, the whole way along they're rounding up millions of Russian militia and laughing at their poor equipment, especially the fact that they transport themselves via horse and cart.

Then the winter hit, the ground froze, fuel froze in the tanks of their vehicles, and the horses were fine so long as they were looked after. Then the Germans got it, hence why a lot of them stole horses to escape the counter-attack from 41 very angry Siberian regiments.

Then you have things like Vietnam, where the military talks about changing the game by using leap-frogging helicopters and all this other new-fangled tech. Turns out it's easy to counter and pretty ineffective if the enemy knows about it, so you start to have a military failure on your hands.

Never discount the tactical validity of something that is said to be obsolete.

But keeping loads of old ineffective stuff around, spending resources on maintaining it that could be spent on something genuinely effective just because it may be useful in a theoretical specific situation that may arise in the future is way to run a military force.

That's how things become obsolete, they don't become completely useless overnight, they become less and less useful in less and less situations until it simply isn't worth keeping around any more. I think it's unlikely we're going to be keeping battle tanks around for another 38000 or so years on the off chance they may come in handy...

And I'm sure it's quite possible to think of a scenario where a mass amphibious assault could happen in 40k, a traitor governor holed up in a fortified city on an island with way too much flak cover to make landing on the same island feasible, for instance (maybe more a job for the Astartes, but there are many reasons why they might not be available). If we can have [URL="http://wh40k.lexicanum.com/wiki/Siege_of_Vraks"]trench warfare[/URL] in 40k, I'm sure you can contrive a scenario for mass amphibious assaults too. Like I said, naval warfare would be a niche and specialised aspect of war in 40k, much moreso than in modern earth, I doubt most Imperial task forces would even bring naval equipment along, but it doesn't mean it has to be absent entirely.

Houghten - Chimeras float but they aren't seaworthy, only good for negotiating swamps and crossing rivers.

I'm loving the idea of Astartes operating underwater in power armour as well, can imagine the having something that looks a bit like a jump pack but with props rather than booster jets to get them around, very cool.

[CoffeeGrunt]

I'm loving the idea of Astartes operating underwater in power armour as well, can imagine the having something that looks a bit like a jump pack but with props rather than booster jets to get them around, very cool.

Space Wolves and Tau do exactly this, the Tau using custom-fitted Crisis Suits and the Space Wolves Drop Podding into the deep then climbing out with custom Jump Packs IIRC.

[completeHook]

In Dan Abnett's Double Eagle there is a massed seaborne invasion, and before that the Chaos forces are using massive land based aircraft carriers to cross a desert.

What's to say that a fleet doesn't have void based elements to it? If you think about it contemporary navies use a combination of surface ships, submarines, aircraft and satellites already. Surface ships in this context are no more impractical than Titans or Leviathans or painting your armour in primary colours and officers dressing themselves up in really fancy hats (sniper rifles are rubbish in the 41st millennium so maybe that's not such an issue).

For use in game terms you could probably just use Master of Ordinance rules (there are more options to represent artillery barrages in one of the Forgeworld Guard lists but I can't remember which one) to represent a coastal bombardment from the fleet. There's a custom Stronghold Assault scenario in there somewhere.

[Katharon]

I can tell you straight up, again, that orbital and space-capable warships or weapon platforms make any form of surface vessel (ie, not a submarine) obsolete. It's like crushing an ant while it scuttles across a large, empty plate.

[Houghten]

Only if the plate's empty.

The justification for having land battles and not just orbitally bombarding is there's something to fight over.

So if you have a sea-surface-based installation, such as a promethium-drilling rig, kelp farm or even a whole Kamino-style stilt city, you'll want a sea-based force with which to defend it.

[Charon]

So if you have a sea-surface-based installation, such as a promethium-drilling rig, kelp farm or even a whole Kamino-style stilt city, you'll want a sea-based force with which to defend it.

You probably will have a void shield, you probably will have city based macro cannons. you would still go by air. You would probably have civillian ships refitted but no actual defence fleet.
Part of the reason is that every attacker (unless we see a civil war) does come from space. So the attacker MUST have a battlefleet.
Battlefleets usually do not carry any ships. Even if they would what would be the advantage over carrying aircraft?

An example for such a battle was Fulgrims fight against the Laer.

[Houghten]

Battlefleets usually do not carry any ships. Even if they would what would be the advantage over carrying aircraft?

Fuel. Staying aloft requires the active expenditure of energy (unless you're a zeppelin), whereas staying afloat is an entirely passive measure. Thus, an aircraft can stay up for a few hours, after which it must either return for home or crash messily. A ship can go for days without refueling (years if it's nuclear).

[Fueldrop]

depending on what sensors are in play, it might be possible to conceal a surface ship from orbital scans relatively easily. Scan for heat? Heat dispersal into the ocean. Visual scan? planets are big! Radar? If it's choppy then that's not going to work, too many false positives. Sonar? Can't be done from orbit. Add in the stealth technology we know is available to the Imperium, and I can see small to medium-sized craft avoiding automatic notice.

The fact is that it's not easy to scan the entire surface of a planet, so most invaders are going to do a general scan for anything that'll indicate a major threat (population centers, radiation hotspots, ect) then focus their attention on their landing zones. The lack of AI really hinders planet-wide scanning.

[Katharon]

Only if the plate's empty.

The justification for having land battles and not just orbitally bombarding is there's something to fight over.

So if you have a sea-surface-based installation, such as a promethium-drilling rig, kelp farm or even a whole Kamino-style stilt city, you'll want a sea-based force with which to defend it.

There is such a thing as a 'tactical bombardment'.