How Royal Marine commandos became standing units

What prompted the Royal Marines to form standing commando units?

Second World War commando operations gave the Navy a reason to organize and train its existing amphibious specialists as permanent formations.

The First World War Royal Naval Division had largely drawn on sailors and reservists, so it was not a direct model for later Royal Marine brigades. In the Second World War, Army commando activity drew attention to troops the Navy already had for raiding and amphibious work. Training these specialists as naval commandos led toward permanent Royal Marine commando formations. The Second Sea Lord receives credit for drawing up the plans, while Reginald Henderson's involvement remains probable because he supported landing craft and landing ships.