Key point: The Barb's effectiveness was born from the U.S. Navy's broader maritime supremacy against Japan.
In the closing months of World War II, heavy losses and depleted fuel stocks kept many of Japan’s remaining combat aircraft grounded and warships in port, awaiting an anticipated amphibious invasion. Starting in July 1945, Allied battleships embarked on a series of naval bombardments of coastal cities in Japan in an effort to draw these forces out to battle—with little success. However, a week before the battleships began lobbing their massive shells, a legendary U.S. submarine toting a rocket launcher began its own campaign of coastal terror that foretold the future of naval warfare—and also engaged in the only Allied ground-combat operation on Japanese home-island soil.
Submarines still made use of deck guns during World War II, most of them ranging between three and five inches in caliber. These were used to finish off unarmed merchant ships or sink smaller vessels that could evade torpedoes—but also were occasionally directed to bombard coastal targets, such as in early-war Japanese raids on the coasts of California and Australia. The problem was that a single gun was unlikely to inflict much damage in a short amount of time, and the submarines were highly vulnerable to air, sea and land attack as long as they remained surfaced.
In 1942, the German Kriegsmarine actually tested submarine rocket artillery that could be fired underwater, but gave up on the idea due to its impracticality. Rumors that Germany had modified their subs to launch V-2 ballistic missiles at the United States led to a vigorous and bloody submarine hunt in the closing weeks of World War II.
The U.S. Navy, meanwhile, considered a much cruder solution: taking one of the Mark 51 rocket launchers it used on some of its LSM landing ships and strapping it to the main deck of a submarine. The twelve spin-stabilized 127-millimeter rockets mounted on the launch rack could only be fired while surfaced, and had a maximum range of three miles. However, a full volley could be ripple fired in the space of five seconds. The fixed launcher was unable to traverse, so the entire submarine had to turn to adjust the aim laterally.