Extra tanks and the scale of warship fuel needs

Are drop tanks or other temporary fuel tanks feasible for ships?

Yes, but the added volume is small compared with the fuel a warship needs.

Ships have carried extra fuel in inflatable bladders and temporary arrangements. The constraint is additional capacity relative to the ship's consumption. Requirements run to hundreds of tons, limiting the effect of small containers. Spaces could also become fuel tanks in wartime once treaty concerns no longer applied. The remembered Iowa fuel-consumption anecdote conveys scale without establishing a reliable figure.