Quick answer
Sierra is the letter S flag: a white field with a blue central square. Its single-letter International Code of Signals meaning is “I am operating astern propulsion.” The Republic of Singapore Navy also publishes this meaning in its flag guide.
| Item | Description |
|---|---|
| Letter and name | S — Sierra |
| Identifying pattern | Blue central square on white |
| Morse equivalent | Three dots (···) |
| Overall proportions | No universal manufacturing ratio verified here |
| Colour specification | Blue and white; no verified physical colour standard or numerical screen palette supplied |
| Construction dimensions | No verified numerical centre-square size, border width or manufacturing tolerances supplied |
Construction and evidence limits
The identification plate in Publication 102 supports the identifying pattern, not a dimensioned manufacturing specification. Do not derive exact proportions or colour values by measuring its artwork. Common manufacture is not established by the evidence reviewed. Screen colours would be approximations; any newly dimensioned drawing would be an editorial reconstruction unless supported by a separate standard.
Signal context
Publication 102 qualifies S: sound use must comply with the collision regulations, and S has a separate meaning in small-boat landing signals for persons in distress. Interpret it within the applicable signalling system.
Historical context
Publication 102 records adoption of the revised Code in 1965 and its effectiveness from 1 April 1969. These are Code milestones, not verified dates for Sierra’s original design. The cited US edition was revised in 2003.
International Code Flag Papa
Compare Papa’s white centre on blue with Sierra’s blue centre on white.