At The Diplomat, Zachary Keck looks at how the evolution of military technology would make future D-Day style invasions much more difficult:
Seaborne invasions are one of, if not the most, difficult kind of military operation. That is partially why, as Mearsheimer points out, the great stopping power of water is so consequential in international politics. At first glance, it might seem like the innovations in transportation and communication technology that have triggered globalization would make contemporary amphibious assaults easier
Not so, however. To begin with, many of the basic challenges that have always plagued seaborne invasions are rooted in geography, which remains relatively fixed. Namely, the defending force in amphibious invasions are usually heavily fortified while the landing force typically has to initially fight in the open. The landing force also remains extremely vulnerable before actually reaching land, especially since the defending force can rely on land-based defense systems.
In fact, as Stratfor, a private global intelligence firm, points out, modern defense technologies have made amphibious assaults much more difficult. The most “significant development” since World War II, Stratfor points out, is precision-guided munitions (these did exist in rudimentary form during the conflict). The analysis goes to explain:
“A contemporary landing force would approach the beachhead in an amphibious landing vehicle such as the U.S. Assault Amphibious Vehicle, which moves at around 13 kph (8 mph). This would be vulnerable to anti-tank guided missiles fired from positions onshore. On D-Day, ships in the Allied invasion fleet were also able to come relatively close to shore to deploy landing craft. The deadly threat of anti-ship cruise missiles in modern warfare would force a modern fleet to remain farther out to sea, leaving amphibious vehicles even more exposed.”
This last point is especially important. As Sydney Freedberg noted back in April, “The new [Marine] Corps concept, Expeditionary Force 21, predicts long-range threats will force the fleet to stay at least 65 nautical miles offshore, a dozen times the distance that existing Marine amphibious vehicles are designed to swim.”
Smaller invasions against undefended coastline — think of both the initial Argentinian attack on the Falkland Islands and the British counter-attack as examples — are still possible, especially in bolt-from-the-blue surprise fashion, but an attack against an active defence with modern weapons might well be unacceptably hard for even the US Marine Corps.