The Termit / Styx has seen a fair amount of combat use. Their first combat action was after the Six Day War in 1967, while the Arabs and the Israelis were taking pot-shots at each other. The Egyptians drew blood on 21 October 1967, when the Israeli destroyer ELIAT approached Port Said, Egypt. Two Egyptian KOMAR-class missile boats, each armed with two P-15 Termit missiles, fired their loads at the destroyer. Three of the missiles scored hits, and the destroyer broke in half, quickly sinking with substantial loss of life; the fourth missile arrived too late to pick up the target.
This was the first effective use of a guided antiship missile in combat. The whole incident was not only a shock to the Israelis, it made Western navies sit up and take notice of developments in antiship missiles. However, the Egyptians didn't get lucky with the P-15 again, since the Israelis quickly developed countermeasures that rendered it ineffectual. There is a rumor that the Egyptians did sink an Israeli SIGINT vessel with the Styx in 1968, but no Western sources confirm this.
In any case, during the Yom Kippur War in 1973, 54 P-15s were fired, with Western sources claiming they made no kills at all. Eastern sources claimed they scored seven kills, but the targets were all small vessels -- trawlers, missile boats, and patrol boats -- and even with those losses taken at face value, it wasn't much of a return on the investment. Worse, the Israelis retaliated against the missile launches and sank seven Egyptian and Syrian vessels with Gabriel I antiship missiles. Both Western and Eastern sources agree on this number of kills. The Israeli countermeasures against the Styx included flying helicopters low and slow over the water so they looked like surface vessels. When missiles were launched they would climb and break radar lock while Israeli missile boats returned fire.
* India employed both these updated P-15U and P-15T versions of the Termit during the 1971 was with Pakistan to good effect. On the night of 3:4 December 1971, Indian Navy OSA-class missile boats were towed to the proximity of Karachi by trawlers. The missile boats fired a total of 11 missiles -- seven P-15Us and four P-15Ts -- sinking the Pakistani (ex-British) destroyer KHAIBAR and a trawler. The Indians also used the P-15Ts against land targets, firing a number of them against the (warm) oil tanks of the refinery at Keamari on 4 and 8 December 1971. The second attack included radar-guided P-15Us, which hit three merchantmen, the British vessel HARMATTAN being sunk and the other two badly damaged.