By 1990, most Army units had replaced their older VRC-12 series FM radios for the new SINCGARS ("SINgle-Channel Ground-Air Radio Systems") family of equipment. Rather than sending a signal along one signal frequency, the SINCGARS radios sent its signals across many frequencies, "hopping" from one frequency to another at high speed. This allowed many nets to share an already-crowded frequency spectrum. Later generations of these radios combined the communications security (COMSEC) encryption devices with the receiver/transmitter, making a single easier-to-program unit. Most significant, the SINCGARS radios could send and receive digital traffic with great fidelity. By the advent of Operation Desert Shield, all Army units were deployed using the most secure FM communications in the world. The SINCGARS radios have a failure rate in extreme heat of once every 7,000 hours compared to the VRC-12 series' failure rate of 2–300 hours.