Second Battle of Port Yokosuka

Plans for the Second Administrative Zone of Japan
Upon ascending to the position of Viceroy within Area 11, Princess Nunnally Vi Britannia made a nation-wide inauguration speech, stating that she wish to establish the second Administrative Zone of Japan (where Elevens can call themselves Japanese and would have equal status with Britannians), that the establishment of the 'Special Zone' was not a mistake, and that they needed a gentler world. Upon hearing this speech, the Black Knights and the rest of the Japanese people view this as another way to lure them into a death trap (see Special Administrative Zone Massacre) and instead insisted on a showdown with the Britannians. However, the problem is that they have no other Knightmare Frames other than the Guren Flight-Enabled Version to battle them. Zero (Lelouch Lamperouge) was shocked at the 'Special Zone' proposal by his own sister and temporarily distanced himself from his organization. However, after having a short conversation with his friends at Ashford Academy, he finally was able to bring himself together and went to assist with the battle that was to unfold.

Battle
Suzaku Kururugi amassed a large naval fleet to pursue the Black Knights in order to help the peace that Nunnally wants so much and came across a tanker with a falsified I.D. in which he identified as the one that belonged to the Black Knights. Suzaku then issue a command for them to come up on deck in 10 minutes or else. However, they didn't follow his command and Suzaku ordered the ships to commence firing on the tanker. Kyoshiro Tohdoh ordered that their submarine should crash dive before the tanker is completely destroyed. Assuming that Black Knights dived underwater following the destruction of the tanker, Suzaku ordered the deployments of the Portman IIs, as well as the firing of ASROCs from the destroyers. Though all the missiles/torpedoes missed their target, their explosions actually ruptured the submarine, causing heavy damage to its structure. Tohdoh insisted that if they moved any further, they would be spotted and that they should just hold out.

This was the moment that Zero intervene and issued orders to fire all torpedoes straight ahead. The Black Knights were at first doubtful, but Kaguya Sumeragi insisted that they should trust him, so Tohdoh went through with the plan and ordered all torpedoes to be fired straight ahead. After the torpedoes were fired, the Britannian naval fleet's radar system discovered the submarine and issued all firings and deployments of the Portman IIs to that exact position. Suzaku then deployed his Lancelot Conquista to capture the Black Knights in case they surface. Under Zero's orders, the Black Knights deployed the "anchors" and braced for "shock." As the Portman IIs went to encircle that position, the torpedoes struck an underwater air-pressurizing system, causing air bubbles to rise to the surface, crushing the Portman IIs and send the dropping depth charges down to them, wiping most (if not all) of them out. The air bubbles then went up to cause all naval ships to capsize (though not completely), as they began to flip over.

Conclusion
Shocked by the turn of events, Suzaku examined the casualties that was dealt, as the Tristan and the Mordred flew over the battle scene. Gino Weinberg ordered all remaining units to follow the Knights of the Round lead and go after the Black Knights. Rolo Lamperouge and the Vincent then flew in, carrying Zero into the scene, as Zero declared a strategic ceasefire and that all Black Knight members would join the Special Administrative Zone of Japan. From that point, all forces (both Britannians and Japanese) withdrew.

Reference

 * The Abandoned Mask
 * One Million Miracles