- "Tokyo must have concluded that a potential cross-Strait war would interrupt Japan's energy supply routes from the Middle East" - Yale Global
- "Japan sees a key sea route, the Taiwan Strait, in danger." - Der Spiegel
- The red route is the shortest path between Singapore and Yokohama. It passes the Luzon Strait (Babuyan Channel and Bashi Channel), not the Taiwan Strait
- The yellow route passes through Taiwan Strait, is obviously a detour from Japan to anywhere, except maybe Haiphong
- For transportation of other materials from SE Asia, e.g. Brunei, the Black route shows that Taiwan Strait is even further away from the ideal route
- Even if Taiwan Strait is more convenient, the availability of the alternative via Luzon Strait deems it "optional" instead of "essential"
Update: US PACOM map agrees with me.
Now, why is Japan so interested in a sea route which is really very marginal to its needs?
A note about Great Circle (geodesic) path:
Since the earth is a sphere and the map is a projection onto a plane (with area distortion), my straight line approach is only an approximation.
To be more precise one needs to use the "great circle" to find the shortest path on a spherical surface. The graph on the right shows the great circle for (see great cicle tool here)
- Singapore -Tokyo (via Luzon Strait): 3324 miles
- Singapore - Makung (Penghu) - Tokyo: 3352 miles (should be longer because the GC path has to cut into Hsinchu, which tanker cannot sail into)
- Singapore - Kinmen - Tokyo: 3383 miles
The last chart is using azimuthal projection from Singpaore, so that every striaght line from the center represents the shortest (great circle) distance, (but lines not passing the centers are not). We can again see the shortest path is closer to the NW tip of Luzon.