Aircraft carriers began as mobile aviation bases

When did aircraft carriers begin serving as mobile bases?

From the beginning: the first seaplane carriers were explicitly mobile bases that set up aircraft operations in suitable bays.

Carrier mobility was not a late doctrinal invention. The earliest seaplane carriers already carried the workshops, fuel, personnel, and support needed to establish aviation operations away from a fixed airfield. They could move to a bay or anchorage and then operate aircraft from that temporary base. Early Italian seaplane carriers demonstrate that the mobile-base function existed from the beginning. Modern carrier operations refine that role rather than creating it.