In case of capture he will destroy.
Should the commanding officer of a vessel be compelled to strike his flag, he is to take especial care to destroy all signals, or other papers, the possession of which by an enemy might be injurious to the United States; and he will keep them so prepared, with weights attached to them, that they will sink immediately on being thrown overboard.
Source: Regulations for the Navy of the United States. 1863. (Washington, DC, 1863): Article 6, Section 5, page 63.