wasn't much room in a Polaris—there were 16 on each submarine. The Ship's Inertial Navigation System (SINS) was developed earlier to provide a continuous dead reckoning update of the submarine's position between position fixes via other methods, such as LORAN. This was especially important in the first few years of Polaris, because Transit was not operational until 1964. By 1965 microchips similar to the Texas Instruments units made for the Minuteman II were being purchased by the Navy for the Polaris. The Minuteman guidance systems each required 2000 of these, so the Polaris guidance system may have used a similar number. To keep the price under control, the design was standardized and shared with Westinghouse Electric Company and RCA. In 1962, the price for each Minuteman chip was $50. The price dropped to $2 in 1968. Polaris A-3 This missile replaced the earlier A-1 and A-2 models in the U.S. Navy, and also equipped the British Polaris force. The A-3 had a range extended to and a new weapon bay housing three Mk 2 re-entry vehicles (ReB or Re-Entry Body in U.S. Navy and British usage); and the new W-58 warhead of 200 kt yield. This arrangement was originally described as a "cluster warhead" but was replaced with the term Multiple Re-Entry Vehicle (MRV). The three warheads, also known as "bomblets", were spread out in a "shotgun" like pattern above a single target and were not independently targetable (such as a MIRV missile is). The three warheads were stated to be equivalent in destructive power to a single one-megaton warhead due to their spread out pattern on the target. The first Polaris submarine outfitted with MRV A-3's was the USS Daniel Webster in 1964. Later the Polaris A-3 missiles (but not the ReBs) were also given limited hardening to protect the missile electronics against nuclear electromagnetic pulse effects while in the boost phase. This was known as the A-3T ("Topsy") and was the final production model. Polaris A-1 The initial test model of the Polaris was referred to as the AX series and made its maiden flight from Cape Canaveral on September 24, 1958. The missile failed to perform its pitch and roll maneuver and instead just flew straight up, however the flight was considered a partial success (at that time, "partial success" was used for any missile test that returned usable data). The next flight on October 15 failed