Fully crewing a guard ship made it an attractive candidate for deployment elsewhere, undermining its local purpose. A port could instead spread the same half-crew across two quarter-crewed vessels and retain two fully rigged, fully stored hulls. To an observer, those ships looked commissioned, making it difficult to tell whether the harbour contained guard ships, active warships, or one of each. That uncertainty strengthened port defence while preserving two reserve nuclei that could receive more sailors in an emergency.
Chapter · 7:24-8:21
Why a port might keep two partly crewed guard ships
Two fully rigged but partly crewed guard ships preserved a dependable local reserve and made it harder for an attacker to judge the port's true readiness.