of October 15, 20 Israeli tanks and seven APCs under the command of Colonel Haim Erez crossed the canal and penetrated into Egypt, taking the Egyptians by surprise. For the first 24 hours, Erez's force attacked SAM sites and military columns with impunity, including a major raid on Egyptian missile bases on October 16, in which three Egyptian missile bases were destroyed, along with several tanks, for no Israeli losses. On the morning of October 17, the force was attacked by the 23rd Egyptian Armored Brigade, but managed to repulse the attack. By this time, the Syrians no longer posed a credible threat and the Israelis were able to shift their air power to the south in support of the offensive. The combination of a weakened Egyptian SAM umbrella and a greater concentration of Israeli fighter-bombers meant that the IAF was capable of greatly increasing sorties against Egyptian military targets, including convoys, armor and airfields. The Egyptian bridges across the canal were damaged in Israeli air and artillery attacks. Israeli jets began attacking Egyptian SAM sites and radars, prompting General Ismail to withdraw much of the Egyptians' air defense equipment. This in turn gave the IAF still greater freedom to operate in Egyptian airspace. Israeli jets also attacked and destroyed underground communication cables at Banha in the Nile Delta, forcing the Egyptians to transmit selective messages by radio, which could be intercepted. Aside from the cables at Banha, Israel refrained from attacking economic and strategic infrastructure following an Egyptian threat to retaliate against Israeli cities with Scud missiles. Israeli aircraft bombed Egyptian Scud batteries at Port Said several times. The Egyptian Air Force attempted to interdict IAF sorties and attack Israeli ground forces, but suffered heavy losses in dogfights and from Israeli air defenses, while inflicting light aircraft losses. The heaviest air battles took place over the northern Nile Delta, where the Israelis repeatedly attempted to destroy Egyptian airbases. Although the Israelis tended to come out on top in aerial battles, one notable exception was the Air battle of Mansoura, when an Israeli raid against the Egyptian airbases of Tanta and Mansoura was repulsed by Egyptian fighter aircraft. Securing the bridgehead Despite the success the Israelis were having on the west bank, Generals Bar-Lev and Elazar ordered Sharon to concentrate on securing the bridgehead on the east bank. He was ordered to clear the roads leading to the canal as