PORTLAND — A fire that crippled a nuclear submarine at a shipyard showed that the Navy had become complacent about safety in industrial settings and put too much faith in land-based firefighters who had never trained to battle a blaze aboard a submarine, Navy investigators concluded.

The investigators also said there was confusion at the start of the May 2012 fire at the Portsmouth Naval Shipyard and that there were two hour-long periods in which no water was being put on the flames.

The conclusions were included in more than 100 pages of documents obtained by The Associated Press via a Freedom of Information Act request.

It took 12 hours and the efforts of more than 100 firefighters to save the Groton, Connecticut-based USS Miami after a worker who wanted to go home early set a small fire that quickly spread. Though the sub was saved, the Navy ultimately decided to scrap it after the repair bill hit $700 million.

The fire severely damaged living quarters, the command and control center and a torpedo room, but it did not reach the nuclear propulsion components. Seven people were hurt dousing the flames.

“Complacency had set in, based on the infrequency of shipyard fires and relative success of fire prevention measures,” the report said. “Also, there was an assumption that the proximity to far more assets, especially federal firefighters, reduced the likelihood of a fire not being quickly contained. This organizational reluctance to prepare for a fire of this scale should serve as a wake-up call — large fires can and do happen in industrial environments.”

The Navy launched a series of investigations that led to recommendations, including the installation of temporary automatic fire detection systems while vessels are being repaired or overhauled.

The full report released by U.S. Fleet Forces Command indicated just how dire the situation became aboard the Los Angeles-class submarine, which was undergoing a 20-month overhaul in Kittery: At one point, officials discussed abandoning their firefighting efforts and flooding the dry dock when it appeared the submarine was going to be lost.

Instead, firefighters battling extreme heat and limited visibility eventually beat back the blaze.

Investigators said shipyard firefighters were unfamiliar with the submarine’s layout and that there was no requirement for certification to battle a fire in a shipboard environment — or even conduct a walk-through to familiarize themselves with the sub. They also said the firefighting force had been reduced, leading to a greater reliance on civilian firefighters.

A regional assessment of the 26-person shipyard fire department was conducted in October 2011 and found them to be fully ready, despite the department having conducted no live fire training since 2006, the report said.

While the report cited lack of readiness by firefighters, the Navy also said it was to blame for failing to incorporate lessons learned from past fires into training.

The report included 99 recommendations — virtually all of which were redacted.

The recommendations apply to ships that are being repaired or overhauled. The report notes that they’re more vulnerable in that setting because the ship’s damage control equipment is removed or inoperable; most of the crew is away; and temporary fire control equipment is less familiar to crew.

The report found that a handful of shipyard workers knew the source of the fire — in a wardroom. But someone pulled a fire alarm in a different part of the submarine, adding to the confusion as firefighters tried to locate the source of the flames.

McDermott reported from Providence, Rhode Island.