(later named the Barracuda class), which entered service in 1951. At 750 long ton surfaced, they were considerably smaller than the 1650 long ton boats produced in World War II. They were equipped with an advanced passive sonar, the bow-mounted BQR-4, but had only four torpedo tubes. Initially, a sonar located around the conning tower was considered, but tests showed that bow-mounted sonar was much less affected by the submarine's own noise.

While developing the purpose-built SSKs, consideration was