WWII Submarine Effectiveness by Nation (1939-1945)

A few months ago I posted an overview of the five largest submarine forces of WWII. That was intended as background for this post and I would suggest reading it before continuing.

As mentioned in my previous post, the focus on the German submarines is only natural given their massive numbers. The growing interest in the American submarine campaign can also be largely explained by the fact that the United States had the second largest submarine fleet by a farily significant margin. However, while larger numbers almost certainly allowed for a greater influence on the course of the war, they say little about the quality of the forces involved. So here are some figures to assist in determining which nation actually had the best submarine force during the war.

Since the most well known contribution of submarines to the war was in sinking merchant ships, we will turn there first.

Gross registered tonnage sunk by each nation's submarines

As can be seen, the German submarine campaign was an incredible undertaking, destroying almost fifteen million tons of merchant traffic across the full expanse of the North and South Atlantic. The American campaign against Japan, while far more successful, was only a third of that size, sinking just over five million tons of shipping. Compared to these two massive efforts, it is no wonder that the work of the other three nations' submarines is so often neglected or even disparaged.

However, because the German and American submarine forces were so much larger than those of the other powers, the above figures are somewhat deceptive when it comes to comparing the actual effectiveness of each navy's submarines.

Total tonnage sunk divided by the total number of active submarines

By looking at average tonnage sunk per submarine, we can get a better idea of what was the result of quantity rather than quality. What stands out is that the American submarines were nearly 50% more effective than the German boats. Still, the Germans were hardly poor performers and were themselves roughly 100% more effective than the British, Japanese, or Italians. All three of the latter actually fell in a surprisingly narrow range given the vast differences in strategy, geography, and materiel.

But these figures still do not tell the full story because submarines did not solely attack merchantmen. Indeed, before the war began, the Americans and Japanese had trained primarily at attacking naval targets. Therefore, we must also take effectiveness against warships into consideration.

During the war, American submarines sank twenty major warships (one battleship, eight aircraft carriers, and eleven cruisers), the Germans sank fourteen (two battleships, six aircraft carriers, and six cruisers), the Japanese four (three aircraft carriers and one cruiser), the British six (all cruisers), and the Italians three (all cruisers). When divided by the number of submarines each nation possessed, we get the following:

The total of battleships, cruisers, and aircraft carriers divided by the total number of submarines

Just as with merchant traffic, the British, Japanese, and Italians all had virtually the same effectiveness against warships while the Americans were far more effective. However, in a striking difference, the Germans sank relatively few warships per submarine. These numbers suggest that the Germans prioritized their efforts against merchant traffic while the submarines of the other four powers split their time fairly evenly between military and economic targets.

This has two key ramifications. First, the Germans submarines were actually no more effective than those of the other powers, they merely focused on a particular target set. Second, contrary to popular opinion, the Japanese did not focus on sinking warships to the exclusion of attacking merchantmen. After all, if that was the case then we should have seen Japan place far below the other powers in the second chart, just as Germany did in the third chart.

These points will show up more clearly in our final measurement of effectiveness below. To calculate this, I multiplied the merchant tonnage sunk per submarine by the number of major warships sunk per submarine.

Tonnage sunk per submarine multiplied by warships sunk per submarine

First, let us address the staggering outlier that is the United States. Unlike the Germans (who performed well against merchantmen and poorly against warships) or the other three (who performed averagely against both target sets), the Americans were around twice as effective as average in sinking both merchant traffic and warships. Thus, when the scores were multiplied, the American score soared while the others averaged out.

However, this can not be simply written off as a mathematical artificiality. As seen in my previous post assessing the submarine fleets of these five nations, the American fleet was inarguably the best of the war, being composed of a large number of powerful and modern boats. Further, the Japanese antisubmarine forces were extremely poor, suffering from significant deficiencies in numbers, technology, and tactics, which allowed the American submarines to enjoy much greater success than they might have against other navies. Thus, while the above number is rather high, I believe that it does accurately reflect the incredible effectiveness of the American submarines.

Looking at the other navies we will also see some rather interesting information. Despite being largely ignored by history, the British submarines scored noticeably better than the Japanese, Germans, or Italians. Given that the British submarine fleet was somewhat underwhelming and spent the majority of its effort in European waters where one would imagine that there were few good targets, this is probably worth looking into further. Also of interest is that the Japanese scored slightly higher than the Germans. Although this may run contrary to the common narrative, it is not that surprising when one considered both the reputation of the Imperial Navy and that Japanese submarines were far larger and more capable than their German counterparts.

While these numbers are far from being the final word on this topic, they allow us to take a second look at the submarine forces of WWII and the narratives that have arisen over the past seventy years. Although the American and German submarine fleets are already undergoing significant reevaluation, placing their histories more inline with the above figures, after researching this post I feel that the British and Japanese submarine fleets deserve far more attention than they have received to date.