Operation Eagle Claw set out in the middle of the night 40 years ago as a mission to rescue 52 hostages held in Iran. Delta Force, Rangers, and Green Berets were flown from Oman to Desert One inside Iran. However, the rescue mission was extremely complicated and did not go as planned. While those involved were the best of the best, they never had the chance to run through the training exercises together and were on different pages. When the troops were approaching the area, several helicopters suffered mechanical issues and could no longer carry the assault force. Then, one of the helicopters crashed into a stationary C-130 on the ground and killed eight service members.
Source: https://connectingvets.radio.com/articles/40th-anniversary-of-operation-eagle-claw