Personally I wouldn't see the RM doing any amphibious assaults either. As has been said, any beach head will be heavily defended, and the only way is to match it with heavy armour, and only the USMC can provide that. Line up a dozen LCACs (and I mean proper LCAC's, not our poxy little things), steam up with troops/light vehicles following on behind in conventional landing craft. The second you hit the beach, pour out the Abrams (each LCAC can carry 4 MBT's I believe) and roll up the sandy road to Baghdad. And seeing as RM could only fulfill the infantry wave part, I doubt there would be any need for their skill. In fact, I'd probably prefer to take the US marines if possible, given they will be far more familiar with the operation style, and correct me if I'm wrong but I'm pretty sure their marines can outshoot ours, handy if the pancake terrain could have them engaging targets at their maximum effective range. Not to mention the fact that a deafening storm of "Hooyah!" "Get some!" "That all you got? My momma can fight better than you!" will keep the civilians back home more happy than "Aww bugger, me boots melted again".
That said, I can forsee the RM being used more once the land battle gets started, perhaps doing commando stuff by taking on forward air defences, command posts and the like. More probable though, they'd be operating in the Northern areas doing their mountain warfare thing, the Iraqi heavy armour would probably be concentrated elsewhere so the light infantry nature of the RM wouldn't be such a problem, especially as the no fly zones would be an excellent starting point for an air campaign, probably speeding up the aquisitation of air dominance over those areas and allowing CAS aircraft relatively free movement to support ground forces.
Going back to the paratroops issue, there is little need to paratroops as a lot of the terrain seems to be suitable for (albeit rough) landing medium and small transport aircraft, so it would be more safe to just land and have the troops on the ground jsut as fast, but with less danger and probably some form of armoured support. Even in this instance, The main purpose I expect would be to cut off Iraqi armoured formations, in which case heavy infantry would be more suited, with more anti tank weapons than you can shake a stick at and in this role again, much safer to land troops with more heavy weapons than they would be able to jump with. The only real use I can see for dropping conventional troops would be to very rapidly secure key resources such as oil installations. The US has apparently got evidence that Iraq plans to destroy key infrastructure elements such as these as they fall back, so we may want to take them as soon as possible before they Iraqis realise they're losing and blow them up. Besides, even if we aren't worried about that, Bush will. No point invading Iraq to control it's oil if it's all burning now is there

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