In 1920 the Texas Navy proposed an ambitious construction program to coincide with the increase in her manpower. The strategists conferred for several weeks and examined their existing structure, their war experiences, and reports on enemy material and equipment. Several shortcomings were determined: first, and most glaring, was the unpreparedness for the requirements of anti-submarine warfare; second, the absence of auxiliaries to provision and maintain ships of lesser endurance; third, that Texas was not likely to enter into a stand-alone conflict in the future, but would more likely be drawn into the wars of her allies; and fourth, the complete underestimation of the potential of submarines as a weapon.
All Texas submarines designed before WWI were designed for coastal defense. The S-3 class, the oldest in active service had a combat radius of less than 400 miles. Their successors, the S-7 class, had a combat radius of just over 500 miles. Their endurance was extremely limited and their role was primarily engaging a hostile fleet if the capital ships failed to halt them.
Reports made after the war, when German U-boats were made available for examination, turned the Submarine force on its collective ear. The enormous potential of submarines beyond the submersible torpedo boat was abundantly clear - in the eyes of the Naval Staff it had been the u-boats that had tied down the bulk of the allied fleets, not the battleships or battlecruisers. Whereas the big guns had ventured out only once for what was an inconclusive exchange at Jutland, the submarines had been a near-constant threat.
Therefore after 1920 Texas subs, taking lessons from both victor and vanquished, are designed for those re-assessed operational requirements. They will have longer range, enabling them to venture into the Atlantic Ocean, carry more tubes and more torpedos, and have better seakeeping characteristics. The first venture on those requirements is the S-9 Class, with two laid down in 1921 and commissioned the next year.
Dimensionally similar to the American S-Class, and built by Electric Boat in the US, they were cosmetically similar to the German UB-III and U-111, which had been examined by Texan submariners after the war. They were single hulled, armed with 4 21-inch bow torpedo tubes and a 3-inch deck gun. They were also fitted with long range radios to enable communications between subs or surface ships. They were expected to have a patrol endurance of 21 to 30 days.
But their similarities to the American S-boats also brought similar shortcomings. The S-9s were hard on their crews, and were not very maneuverable in spite of their large rudders. With a full load of torpedoes their bows did not ride waves as gracefully as hoped, swamping the deck gun and making it unusable in anything but a calm sea.
But they were the first step to changing undersea warfare for the Texas Navy. Classes designed to similar characteristics were constructed and within a few years, the older coastal boats were replaced or relegated to training duties at the Submariners School.