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Monday, June 13, 2011

Sea Lines of Communication or Sea Lanes

Back in the beginning days of this blog, I had a couple of posts about "sea lanes" and their importance. For example, from 2005, there was a post cleverly titled "Sea Lanes". I wrote then:
I keep posting about sea lanes. What are these things? Sea lanes are trade routes - almost like highways in the sea, where due to geography, ocean going vessels follow certain paths to avoid islands, shallows and other impediments to their travel. They are also generally the most efficient routes to get from Point A to Point B - as close to straight line travel as a ship can accomplish given the number of obstacles in its path.
Since then, there have been hundreds of posts here in which I refer to either "sea lanes" or "sea lines of communication" (see, e.g. Sea Lines of Communication (SLOCs)). There can be a difference between the two terms, since SLOC can have a military meaning that I have generally ignored here.

However, what is important to know about sea lanes or SLOCs is that they exist and that they are a major reason that nations interested in international commerce have navies - to keep the sea lanes open. In discussing maritime security, keeping sea lanes open is a major topic.

We hear a lot about how many things travel by sea. From crude oil to grain to large screen TVs to cars and much more, cheaper shipping has allowed the entire world to benefit from global product distribution (see here and here). Where do these products travel? Sea lanes. An excellent example of these sea lanes is shown on this Naval War College slide (which I have borrowed without shame):

There it is, a picture of world commerce. Those are not war ships wending their way across oceans, those are merchant ships moving the goods that make the world go. You might note that there are places where the traffic converges to pass through narrow areas. These are referred to as "chokepoints", "Chokepoints are narrow channels along widely used global sea routes . . ."

Large ships sail on rigid schedules, carrying parts from Japan to the U.S. or to Europe in such a reliable manner that warehouse costs are reduced by planning for "just in time" deliveries of products.

So, when there is a disruption in the smooth flow of goods, say from the recent earthquake in Japan, there are ripple effects that impact more than the Japanese part manufacturers.

A similar effect is caused by things that interfere with sea lanes. These might be something like a catastrophe that strikes a chokepoint like a closure of the Suez Canal.

Taking the map above, I added some blue arrows to point at a few chokepoints, like the Suez Canal, Strait of Malacca, Strait of Hormuz, Strait of Bab el-Mandab, Strait of Gibraltar, and the general area of straits leading from the Caribbean into the Gulf of Mexico (see below).

Want to look at Caribbean chokepoints? I added some destroyer images to make the point - most of the oil imported into the U.S. by ship has to pass through these straits. In turn, these straits need to be protected if our economy is to work.

Finally, let me again refer to an older post about the Somali pirates and how cleverly they've been in moving out into the major sea lanes of the Indian Ocean area as they ply their trade. See Where the Somali Pirates Operate and Why where I put up this consolidated image of the Indian Ocean sea lanes and pirates strikes:

While there seem to be logistical limits on the Somali pirates as to the number of captive ships and hostages they can host at any given time and this limits their impact on the sea lane flow of commerce, they are certainly well-versed in the exploitation of the known sea lanes. Even this relatively minor bump in the flow of traffic, though, has been enough to get 20 or more naval vessels from many different countries out into the Indian Ocean attempting to thwart interference by the pirates of these vital sea lanes.

The greater lesson of the Somali pirates is how relatively easy it may be to cause trouble on sea lanes or at chokepoints and why it is vital to have in place assets to counter any such attempted trouble making.

We have now reviewed sea lanes, sea lines of communication and choke points and their importance to the global flow of commerce on the highway of the sea.

I suppose we also have covered why we, a nation dependent on maritime commerce, have a Navy and a Coast Guard out there keeping the sea lanes open. As noted here:
70% of the world is water, 80% of the world lives on or near the coastline and 90% of our commerce sails across it. Any disruption in that chain caused by instability has a direct impact on American quality of life.


  1. a very good article!

    The Main point for the USN is that they do NOT have to search the Indian Ocean, they only have to control access to/from certain ports and some sea control. One wonders is these details have light a fire under anyone in the Obama asministration?

    Try to superimpose China's" String of Pearls" onto it and even more strategic relevance may appear?

  2. eastriver1:09 PM

    Bravo. It would be magnificent if every member of Congress would be compelled to memorize this post.

  3. It would be magnificent if no member of Congress ever needed to read this post, as the Navy and Marine Corps had already taken care of the problem at it's root without oversight and interference.

  4. I'm sorry, if I could be allowed to amend and extend my remarks. An excellant post which I will pass along whenever possible.

  5. Great blog. You might also find it interesting to compare SLOCs to the global information flows--most international business information travels the globe through transoceanic cables, and the cables generally follow the flow of shipping traffic (see the great maps from telegeography, particularly

    Two notable exceptions: there's no traffic around South America (it all goes overland through the US instead), and there's little traffic around the Horn of Africa (it goes through the Suez Canal).

    The maritime mission has always been to protect SLOCs, but I wonder if there will come a point when protecting SLOCs also means protecting our transoceanic communications infrastructure?