Cerberus was meant to remain in a strategically important harbour, far from the Royal Navy's main fleet. Her guns and armour forced any raider seeking a quick local victory to deal with a heavily armed guardship first. Victoria could therefore field some local strength without funding a force built for long-range operations. The arrangement concentrated limited colonial resources at the place they were expected to matter most.
Chapter · 3:52-4:50
A guardship built to stop a quick harbour seizure
Cerberus gave Victoria a concentrated local defence against a quick attempt to seize its harbour without requiring a blue-water fleet.