How to shut down an enemy harbor

The objective of the Japanese attack on Pearl Harbor was to eliminate the United States Navy's Pacific Fleet as an effective fighting force. This would enable Japan to take the Dutch East Indies and secure China without effective opposition. As history shows, however, that didn't work out too well for Japan. But there are effective ways to keep an enemy fleet bottled up.

One of the best methods is to make moving out of a harbor a hazardous venture. There are a few ways to do that – one is by parking subs outside the harbor and firing torpedoes at any ship that comes in. The problem here is that the subs can be sunk or driven away — and the enemy fleet is now out and hunting your ships. There is, however, a much more long-lasting way to keep enemy ships in their harbor that doesn't risk a sub and its crew.

You lay mines. It can be done many ways, but you're best off using submarine-laid mines or air-dropped mines. The submarine approach is best for when you don't want the enemy to know what's in store. Something going boom quickly tells the enemy that this isn't a bluff. Submarines can carry two mines for every torpedo and can quickly shut down an enemy harbor, even if they can't carpet the entire area. 

The other option is to drop the mines from planes. This is a significantly more conspicuous method but, as Tom Clancy commented his book Submarine, sometimes, all you really need is a press release. Watching mines get dropped into nearby waters is sure to shut down movement. Today, the primary air-dropped mines the United States uses are the Quickstrike series – modified dumb bombs.

Here's what makes using those mines extra appealing: A B-2A Spirit can carry a few dozen 500-pound bombs in a single sortie, and a Mk 62 Quickstrike mine is little more than an Mk 82 bomb with a different fusing arrangement. 

The use of air-dropped mines has a long history and was used prolifically during World War II.

Check out the video below to see some historical, airborne mine deployment.