Remember Britain is a world power even with its power starting to wane in the 30s. Britain has its colonies and dominions to call upon in case of war. This brings a lot of manpower and resources to its country. The longer the war goes, the more time Britain has to mobilize its forces. Now you could say Germany could sink its transports ships and convoys but Britain won’t stand idly by to let that happen. It still has its powerful navy to call on and the industrial might of the UK can make more ships. The UK isn’t helpless, it got knocked down but it could still fight and survive.

To answer the question of why Germany couldn’t invade Britain is because Naval invasions are complicated. You need a few things before you naval invade anywhere; you need Naval superiority, Air superiority, and to plan and prepare your forces.

Naval superiority takes years even decades to properly prepare. The Germans Kreigsmarine suffered heavy losses after Operation Wessrubung losing 1 heavy cruiser, 2 light cruisers, 10 destroyers, a few subs, and many transport ships. The forces it had left were minuscule which was 3 cruisers and 4 destroyers;this could not compete with British Home fleet. The Home fleet consisted at 1940 5 Battleships, 1 carrier, 11 cruisers, and 8 destroyers. You need a surface fleet to protect your transports from warships and subs which would devastate these transports. You need a fleet to protect your supplies and reinforcements to the beach head. Germany would have to now focus on building and training a fleet to establish Naval superiority. This would take precious resources that Germany doesn’t have. They would have to neglect other aspects of their war economy like tanks and planes to build this navy up. And even then this would take years of building these ships and by that time who knows how much Britain has built up their forces?

Air Superiority is a new requirement but still very important to the operation. While Germany had sizable air force and was well experienced, the RAF was no push over. We can maybe look at the Battle of Britain as what might have happened, albeit with higher casualties on the British perhaps. However Air superiority is not a constant, it can change constantly and must be maintained. The question is then who could maintain it? Who could afford the losses and who could not. The answer is the British could afford such losses, but Germany could not. You can see this in the Battle of Britain with Germany losing a lot of aircraft but not replacing them, while the British were replacing the aircraft losses. Germany can’t afford a war of attraction, it’s on the clock and must end the war fast.

Which brings me to planning and logistics. Germany needs to have planned out every little detail of this invasion. Where will they invade? Where is the nearest port? Where are the defenses strong and where are they weak? What should be their first day’s objective? If they can’t get a port, how will they resupply? And this is just the initial invasion, what happens if they make a beachhead? It could easily be pushed back into the sea if not properly reinforced and established. The most vulnerable a naval invasion is when its first disembarking and establishing a beachhead. The list goes on and on for what they need, but the point I’m trying to make is that this takes time. Germany just can’t invade after Dunkirk or the Fall of France, it needs time to prepare. And it does not have time or resources for a large scale invasion. Plus with the Soviet Union ready to strike at Germany in the future, Germany has other threats to worry about.

Germany has two choices: to try and invade the UK, probably fail and waste resources. Or invade the Soviet Union who had just stumbled in the Winter War, and secure the natural resources Germany desperately needs.

Sources:

Ferris, J., & Mawdsley, E. (2015). The Cambridge history of the Second World War. Volume 1: Fighting the war. Cambridge: Cambridge University Press.