To compensate for the weaknesses of Egyptian air power, the Egyptians developed their air defenses. They fielded immobile SA-2 and SA-3 SAMs, the backbone of the air defenses, as well as mobile SA-6 SAMs and ZSU-23-4 SPAAGs (Self Propelled Anti-Air Gun), portable infantry SA-7s, in addition to thousands of conventional anti-air artillery. These air defenses would provide a protective "umbrella" over Egyptian ground forces. However, the SA-2 and SA-3 systems, being immobile, could only be moved over a nine-hour period at best, exposing the air defenses to degradation in case of a redeployment to keep up with advancing forces. On the other hand, the SA-6 systems were available in limited numbers insufficient to provide adequate protection to advancing armored forces.