If the army would not participate, naval divisions and the Royal Marines offered an alternative source of troops. That proposal still involved a landing force fighting ashore. Forming and assembling it required time, as did preparing the ships. An instruction to attack immediately would prevent those preparations, regardless of whether the troops came from the army or navy.
Notable Point · 5:23-5:52
Naval troops still needed preparation time
Naval divisions and the Royal Marines offered an alternative source of troops if the army would not participate, provided there was time to prepare them.