The substitute pennants are used when alphabetic flags or numeric pennants need to be repeated in a signal. The 2nd substitute pennant is used for the second flag in the hoist. It also means the absence of chief of staff (Inport).
From the International Code of Signals, this long-lasting nautical flag is made from nylon fabric with double-stitched seams, canvas heading, and ash toggle. This flag is sewn to order.