The 10 American sailors were on an unfamiliar assignment and running behind schedule.

Setting off from Kuwait en route to Bahrain, the U.S. sailors had never navigated across the Persian Gulf in small patrol boats, and they were unaccustomed to traveling such a long distance in vessels designed for shorter missions in coastal waters or rivers.

Their routine mission on Jan. 12 turned into a nightmare when they strayed into Iranian waters near Farsi Island in the Persian Gulf. Members of Iran’s Islamic Revolutionary Guard Corps (IRGC) surrounded the two U.S. boats and made the crew members kneel in surrender with their hands on their head. Iran released a video of the humiliating scene and held the sailors for 16 hours, before a flurry of phone calls between top diplomats in Washington and Tehran secured their release.

The incident, which remains under military investigation, has raised troubling questions not only about the crew’s performance but also about the U.S. Navy’s operations and readiness in one of the world’s most strategic and volatile waterways — where American ships have sailed for decades.

Mechanical problems, communication breakdowns, and a lack of navigation training or preparation all played a role in the blunder, Foreign Policy has learned, based on interviews with officials and others familiar with the case.

Coming just days before a landmark nuclear agreement with Iran entered into force, the capture of the sailors carried the potential to escalate the situation into a full-blown international crisis. And the incident turned into a political firestorm in Washington. Critics of President Barack Obama’s approach to Iran have seized on the administration’s handling of the incident and its aftermath, citing it as further proof that Washington is pulling its punches with Tehran and withholding details from lawmakers.

Officials told FP that the results of an initial U.S. Navy investigation into the case were turned over this week to the commander of the 5th Fleet, Vice Adm. Kevin Donegan, who oversees naval forces in the Middle East. The commander has 30 days to review the findings, decide if more investigatory work is required, and recommend if the crew members or their superior officers should be prosecuted or reprimanded. Other senior officers will then review those recommendations, culminating with a final decision by the Navy’s chief or deputy chief.

Several people — including Obama administration officials, congressional staffers, and others familiar with the details of the incident — discussed the case with FP on condition of anonymity due to the ongoing investigation.