Actually there have been several instances of naval combat in Wh40k, off the top of my head those that come to mind are the battle of Helsreach where Orks assaulted a dockyard from the black sea and another case involving Ork Submarines and a dreadnought wading into shallow waters to take it out. As for a beach assault, in one of the Commissar Cain stories an Ork Waaaagh manages to assault another continent by building a ramshackle armada and landing craft made out of scrap and Gunboats. The Problem is the devs would have to get creative and make their own ships and stuff because GW hasn't released any official models or pictures of naval units. The Orks would be easy to create but the Space Marines would have to utilise some sort of Imperial Battle Frigates or something. Although to not cause any drama for the fans of this site, why not allow the community a competition to design some amphibious vehicles.
Well at least naval combat would be really easy to do compared to space combat. Just it will be like a vehicle on ground just on water.
. Well I heard imperial naval vehicles are actually land raiders and stuff. Most of the land vehicles can go into water.
There's a Blood Angels novel where they commandeer a special Imperial Sub in order to infiltrate Fabius Bile's base. PDF's have navies and air forces. Sometimes they're mainly, or all, just one or the other. I voted yes for ports, including transit ports, because there has to be ways between continents and it will be fun fighting over them especially if they provide other strategic boosts to an army.
Orks and Imperial have sea ships, but I've never heard of chaos or Eldar using them. Though the beach assaults could be a nice little tribute to D day. So i'm not skeptical for this kind of combat. As long as we get bombers, artillery strikes, and machine gun emplacements that is. All i know is that there will be blood. LOTS OF BLOOD.
Have you seen the Dark Eldar Raiders? They are based on what passes for ships in the old Eldar empire. Craftworld Eldar use something similar, just not as tanks. Chaos Marines either use whatever is at hand or a Daemonic equivalent.
The Imperium vessels are very akin to Ironclad versions of WWII vessels. Large and powerful prows with over sized weaponry and flying GERMAN! Aquila banners all over the place. The Chaos use basically the same types of vessels but tend to be more super sized. Look at the novels by Dann Abnett. In the one named Double Eagle the Chaos forces had a massive Submarine Aircraft Carrier from which they kept spamming fighters from to attack the Imperials. In the novel Flesh and Iron by Henry Zou, the Sisters of Battle had commandeered an entire Imperial Naval task-force. The Eldar basically don't need naval craft because you know....grav skimmers...get on their level. While they might be light and prone to being destroyed by dedicated anti-vehicle weaponry, they're still faster and more agile than any other faction can field in addition to being shielded or cloaked at times. Orks can literally do whatever the hell they want because they defy logic. If it can float, be turned into a weapon, or otherwise ruin your day...it's in their arsenal.
Voted for number two, though i love the fuck out of beaches! Should have really put that option too. On topic, i think naval battles arent really a too much covered thing in 40k (yes a mention here and there, but still very small), so id have to say no. Or if they ever wanna go that alleyway its gonna take years and years for it to come to pass, as basically anything else in 40k really takes priority over naval battles.