The investigation has not yet been released, but CNN spoke with a U.S. official directly familiar with the details. Because the sailors and other naval personnel could be facing disciplinary action, the report may not be released until their fate is settled.
During the time they were held, they were blindfolded and repeatedly separated and interrogated, CNN has also learned.
Members of Iran's Revolutionary Guard Corps naval units captured the sailors on January 12 when six of their armed vessels surrounded two U.S. Navy riverine boats.
According to the report, the sailors originally set out from Kuwait for Bahrain but quickly -- and unknowingly -- went off course and headed almost directly for Iran's Farsi Island in the middle of the Persian Gulf.
The report found that several factors may have contributed to the failure:
- The sailors had never made the trip before.
- They had been up most of the night before conducting maintenance on one of the boats that had broken down.
- They had to "cannibalize" parts from a third boat in order to have two working vessels.
- They then experienced problems with their satellite communications gear.
All of this led them to leaving port later than planned.
In addition, they did not conduct a standard operational briefing for themselves prior to setting sail, during which they would have had fully reviewed their route and navigation plan.
The approved navigation path would have had them sail in international waters between the Iranian coastline and the eastern side of Farsi Island as they moved south toward Bahrain. Instead, they were significantly off course, sailing on the western side of the island.
The report also indicated that the sailors were not aware of Farsi Island's location. They instead believed a small Saudi island was the navigation feature they were supposed to be sailing around.
As the sailors unknowingly approached the Iranian island, they had already missed one scheduled check-in phone call with their command center, and the command center for some reason did not notice that the tracking equipment on board had them headed for Iranian waters.
Once inside Iranian waters, the boat with the navigation problem broke down again and was then fixed.
But the sailors were quickly surrounded by two initial IRGC boats and didn't immediately understand they were Iranian forces, according to the report. Four more IRGC boats quickly approached and encircled the Americans, blocking their escape path.
At this point, the U.S. personnel decided not to resist, seeing no way out of their situation.
The sailors were all put on one boat and ordered to their knees with their hands behind their heads. Video of that was seen around the world.
Then all the sailors were blindfolded except for the two U.S. Navy coxswains who were in charge of sailing the boats into a small lagoon at Farsi Island while guns were still held against them.
Once on Farsi, the sailors were blindfolded and then moved around the building in which they were held. Each was questioned separately and asked about their missions, their boats and what they are doing at sea.
Eventually, all 10 were taken into a large room also seen in a video, and given food. At this point they were told by the Iranians to "act happy" for the camera, the U.S. official said.
The sailors said they argued back and told the Iranians they wouldn't do it. At that point the lieutenant, the senior U.S. person there, said he was sorry for the error in order to defuse the situation, the official said.
The sailors were released the next day by the IRGC after the unit that was holding them was told to release them by senior Iranians, the U.S. official said.
The sailors still may be reprimanded for their actions. And others may be held accountable for faulty training and failure to quickly understand that the boats were on the wrong navigation path and headed for Iran.
The report now goes to senior commanders for review and possible action.