US sailors who were captured in January after straying into Iranian waters committed basic navigational blunders, were quick to surrender and some buckled under questioning, a damning Navy probe released Thursday found.

The report into the January 12 incident in the Persian Gulf highlights a string of leadership and procedural failings in Iran's humiliating seizure of the 10 American sailors, with investigators saying the crews of the two captured boats had been derelict in their duties.

The sailors at times appeared haplessly lost at sea, with the engineer on one boat even resorting to an app on his smartphone to try to figure out the name of an unexpected land mass -- which turned out to be Iran's Farsi Island -- only to find his phone displaying only a "long Arabic name" and no other information.

In all, nine Navy personnel -- three of whom were actually on the boats that were meant to head from Kuwait to Bahrain -- have been disciplined or will face disciplinary action.

Iranian media broadcast humiliating images of the US sailors during their detention, showing them kneeling on their boats at gunpoint with their hands on their heads.

At one point during detention, a gunner from one boat thought about trying to escape, but "did not think of himself as a prisoner of war because the conditions were too nice," the report states.

Though the sailors were held for less than 24 hours, the incident was a major embarrassment for the US Navy and President Barack Obama.

The United States carefully avoided escalating the situation, maintaining a conciliatory tone with Tehran days ahead of the implementation of a historic international deal over Iran's nuclear program.

"I didn't want to start a war that would get people killed," the crew's captain told investigators in explaining why he had quickly surrendered.

"I made the gamble that they're not going to (take us to) Tehran and parade us like prisoners of war, because they want this nuke deal to go through."

- Name, rank, serial number -

Some of the crewmembers told investigators they were subjected to "aggressive behavior" by the Iranians, such as an interrogator "slapping his hand down on the table, spinning a crewmember's chair around or threatening to take a crewmember to Iran for lying."

Sailors told Iranians their name, ranks, serial numbers and dates of birth. Some "played stupid" and evaded answering questions, but others revealed sensitive information such as passwords to their personal phones and laptops, the report found.

The Navy has slammed Iran for detaining its sailors, for hampering their "innocent passage" of Farsi Island and for using them as propaganda tools when it filmed them surrendering and while in captivity.

But the investigation "found a lack of leadership, a disregard for risk management processes and proper mission-planning standards," US Vice Admiral Chris Aquilino told reporters.

"If the guidance provided ... had been followed, this event could have been prevented."

- Lost at sea -

The ill-fated mission was destined for trouble from the get go, the report found.

Originally, the two boats were supposed to go from Kuwait on a 259 nautical mile (480 kilometer) trip to Bahrain, the longest such sailing the crews had ever conducted.

But the mission got off to a late start, so the crews attempted to take a shortcut to make up time, investigators found.

This "deviation" caused them to unknowingly enter Saudi Arabian waters, and then stray into Iranian territorial seas off the coast of Farsi Island. The sailors saw "land masses" but did not realize where they were.

"Crewmembers speculated as to whether these were Saudi Islands, rocks or oil platforms," the probe states. "None of the crew believed that any of the masses were an Iranian island."

The crews had functioning navigation systems, but failed to zoom in to the right level of magnification, the report found.

Less than two miles from the island, one of the boats broke down and stopped in the water.

As crews worked to fix it, two Iranian Revolutionary Guard Corps Navy vessels approached with their guns uncovered. Shortly after, the Americans fixed the mechanical problem and attempted to flee, only to be blocked.

The crews would have been operating within rules of engagement to offer armed resistance, but the captain decided to surrender in order to de-escalate tensions.

The 10 sailors were taken to Farsi Island, where they were interrogated and spent a fitful night.

Eventually, the crew's officer made a scripted apology in saying the incident was the Americans' fault and that the Iranians' behavior had been "fantastic."

The Navy has already relieved three officers of their commands, one of whom was on one of the boats.

Six other people in the case face non-judicial punishments.