Japan joins the Allies and follows Taranto at dawn

What changes if Japan joins the Allies in June 1940 and sends carriers to the Mediterranean?

A Japanese dawn strike after the British night attack at Taranto could devastate the already disordered Italian fleet.

Illustrious and Eagle could deliver the night attack, after which Japanese carriers would arrive while Italian crews were moving ships, fighting fires, and organizing repairs. A daylight follow-up by experienced Japanese dive- and torpedo-bomber units could turn temporary damage into the destruction of much of the battle fleet.