As with so many aspects of the uniform designs of the United States Navy, the introduction of hard shoulder boards was the result of a compromise between the pragmatic and the stylistic.
The years following the Civil War saw the United States Navy take a central role in American military strategy and foreign policy, with its ships on hand to protect the safety of Americans—both diplomats and private businessmen—who were seeking to expand trading relations with many nations, particularly in Asia. One consequence of the Navy’s increasing presence in the Far East was the need for a service white dress uniform, which was introduced with a fly front in 1886. But the climate and other factors meant the coats underwent a rather prodigious amount of laundering, which naturally had a deleterious effect on any rank devices sewn on to the uniforms.
To address the problem, removable buttons replaced the fly front, and rank insignias were placed on shoulder boards that could be quickly and easily removed before washing.
Navy regulations stipulate that, for Line Officers, the surface of the hard shoulder board is to be black. Gold lace stripes that match the number, width, and spacing of the sleeve stripes are used for rank, with the first stripe starting one-quarter inch from the widest end of the shoulder board (the only exception is one-half inch for Ensigns). The Line Corps star is placed on the board the same distance that is specified for the star on the sleeve to be from the stripes found there.