The rope and anchor is a symbol which has been used by the U.S. and other navies for centuries. It's seen on crests and insignia, documents and uniforms, particularly cap badges and the metallic buttons of naval officers' jackets.
The first recorded use of rope & anchor symbolism was by the Lord High Admiral of Scotland in 1402. The symbol was subsequently adopted by the English Navy which, after the union of Scotland and England, became the British, Royal Navy.
The U.S. Navy states: "The fouled anchor (rope- or chain-entwined) so prevalent in our Navy's designs and insignia is a symbol at least 500 years old that has its origins in the British traditions adopted by our naval service."
The symbol of an anchor with a rope (or chain) entwined around it is also known as the fouled or foul anchor, an anchor tangled up in this way being very difficult to raise. The U.S. Navy believes that, despite this negative association, the rope and anchor, both so identified with ships and seamanship, were also used as a joint symbol simply because they make a very decorative image.
The anchor as a symbol of real and spiritual commitment and steadfastness goes back at least to Biblical times. As Hebrews 6:19 reads: "Which hope we have as an anchor of the soul, both sure and steadfast."
The anchor as a symbol of Christian belief and commitment is also reflected in the great 19th century hymn "Will Your Anchor Hold in the Storms of Life?"