US provided satellite intelligence to Iraq pinpointing Iranian targets. The US was far more pissed off at Iran for deposing the their lackey (shah of Iran). and of course the embarrassment of the hostage taking provided additional impetus. Why would the US provide weapons to Iran? Although I do recall a deal was brokered by Bush senior to send weapons to Iran provided they held the hostages until after the 1980 presidential election. The hostages were released the next day after Reagan was elected. Perhaps this is what you were referring to.