What is flown outboard at the starboard yardarm when there is no flag officer's pennant on the ship?

When there is no flag officer's pennant displayed on the ship, the First Substitute is flown at the starboard yardarm. The First Substitute serves as an indication that a flag officer is not on board, essentially informing anyone observing the ship that the expected senior command is temporarily unavailable.

This practice is part of the established naval signaling protocol and helps maintain proper communication and acknowledgment of command presence within the fleet. Each substitute pennant designates a specific situation regarding the absence of flag officers, reinforcing clarity in naval operations.

While the other substitutes (Second, Third, and Fourth) represent different circumstances—such as the absence of other senior officials or specific indications related to the ship's operational status—they do not equate to the same direct implication of a flag officer's absence as the First Substitute does. Hence, the choice of the First Substitute is integral to signaling appropriate information in naval tradition.