Unrestricted Submarine Warfare

Tuesday, April 19th, 2016

The U.S. Navy went into World War 2 with a three-phase plan for handling the Japanese, War Plan Orange:

  1. Pull US Navy ships back to their home ports, and sacrifice outposts near Japan — the Philippines and Guam.
  2. With superior force, advance toward Japan, seizing Japanese-occupied islands to establish supply routes and overseas bases. The US, with its superior production power, should be able to reclaim the Philippines within two or three years.
  3. Choke Japanese trade and bombard the Japanese home islands without invading them.

Submarines were seen as auxiliaries or picket ships that would scout ahead of the fleet and extend its range of observation, but that role ended up being filled by aircraft.

War Plan Orange wargames rarely dealt with submarines substantially; the focus was on battleships versus carriers.

But the U.S. Navy wasn’t able to follow through on War Plan Orange and instead started by ordering unrestricted submarine warfare against Japan’s sea lines of communications:

American Navy planners had not totally overlooked unrestricted submarine warfare in 1940 and 1941, but had given little thought to exactly HOW these operations would be carried out. The Navy had not thought out the necessary components for such a campaign, because it went against Mahanian principles which stressed decisive surface battles. The post-war assessment from inside the submarine community was telling: “Neither by training nor indoctrination was the U.S. Submarine Force readied for unrestricted warfare.” Campaign pressures and operational realities would force the Navy to adapt its plans and way of fighting.

Clay Blair observed that because of its lack of doctrine and working weapons, the U.S. submarine offensive did not truly begin until 1944. Up until then it “had been a learning period, a time of testing, of weeding out, of fixing defects in weapons, strategy, and tactics, of waiting for sufficient numbers of submarines and workable torpedoes.” More boats, more aggressive commanders, reliable torpedoes, and better radar/sonar all made their contribution. By the end autumn of 1944, the period of learning and adaptation was over. The American sea wolves were numerous, trained, and well-armed.

As the war drew to a close, the role of the submarine as an offensive weapon was evident. The boats had served as the principal source of attrition for the Japanese economy by targeting Japan’s commerce, especially its oil tanker fleet. Once the Americans had taken positions in the Philippines, Guam, Midway, Saipan and Okinawa, U.S. forces had cut off the Empire’s energy supply. Strategically, the war was essentially over. Japanese economic productivity was grinding to a halt. Japanese tankers were delivering only one tenth of the oil needed for 1944-45.

After the war, there was agreement among Navy leaders that submarines had played a major role in countering Japan. Nimitz, after some distance and reflection in retirement, said: “During the dark, early months of World War II, it was only the tiny American submarine force that held off the Japanese Empire and enabled our fleet to replace their losses and repair their wounds.” More objectively, speaking well after the war, Admiral “Bull” Halsey observed, “If I had to give credit to the instruments and machines that won us the war in the Pacific, I would rank them in this order; submarines, first, radar second, planes third, and bulldozers fourth.”

The judgment of Navy leaders was validated by post-war government assessments. As noted in the US Strategic Bombing Survey, the impact of the submarine attrition warfare was strategic in effect:

Instead of the 28,500,000 barrels of oil its leaders expected to import from the Southern Zone in 1944, it imported only 4,975,000 barrels. In 1945 its imports were confined to the few thousand barrels brought in during January and February by single tankers that succeeded in running the blockade….After the battles of early 1945, when Japan lost the Philippines and Okinawa, United States forces sat astride its vital oil life line. Strategically the war was won.

This history makes one wonder what the U.S. Navy might have achieved if it had invested the same intellectual capital into developing Fleet submarines and working torpedoes that it had in the carrier. Could the United States have choked off Japan’s trade by the summer of 1943?


  1. Generally speaking, such single-thrust strategies are less effective and efficient than an initial analysis might suggest. For one thing, some proportion of the resources devoted to one strategic path can’t simply be redirected to another. For another, it wonderfully concentrates the mind (and resources) of your enemy upon the defeat of that single thrust. As Joseph Fouche noted on the old CoPS blog, successful strategy requires a significant degree of redundancy.

    In the specific case of submarines vs. carriers, etc, one must keep in mind the basing requirements of the submarines (which will limit their ability to loiter in the core regions of the Japanese empire), the high probability that such a single-effort strategy will prompt the Japanese to actually pay attention to ASW and commerce-protection (which they largely ignored in reality), and that it will prompt the Japanese to develop alternate means of servicing their island garrisons (e.g. large aircraft).

  2. Adam says:

    Could someone clarify Admiral Halsey’s point about the vital role of bulldozers in the war in the pacific? Specifically why they rate alongside submarines, airplanes and radar?

  3. Isegoria says:

    I believe the bulldozers were for building airfields — or unsinkable carriers.

  4. Isegoria says:

    Coolbert of Military Analysis adds this:

    With regard to number four [bulldozers] we are speaking of the naval Construction Battalions. SeaBee’s [CB].

    American advance across the Pacific in the aftermath of the Battle of Midway greatly facilitated by the actions of the CB’s.

    At least within the Pacific Theater able within a period of two weeks to take an island pristine jungle wilderness and construct an airfield and all impedimental associated with same, a port facility and all impedimenta associated with same, barracks, mess halls, hospitals, etc.

    CB personnel for the most part already trained and experienced trade union craftsmen upon entering the military. Trade unionists now wearing a uniform and highly qualified in their respective craft. Trade unionists to include carpenters, plumbers, electricians, masons, iron workers, and heavy machine operators.

    Officers for the most part having civil engineering degrees and also experienced at their profession.

    Officers and enlisted both merely given a mission and the raw material, and told to go. And did so with panache’ for which all ‘Americans can be most grateful.

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