Injured navy sailors and families of those killed in the 2017 collision between an NYK Line boxship and the warship USS Fitzgerald are suing the Japanese shipping giant in litigation seeking $265m.

In two lawsuits, both filed in New Orleans federal court this week, the 39 sailors hurt and the families of the seven killed accuse the 2,854-teu ACX Crystal (built 2008) of causing the US Navy's greatest loss of life at sea since 1975.

That is a conclusion that differs from the findings of both the navy and the Japanese accident investigators, which cited failures by officers watchstanders on the warship as a potential cause of the incident.

Injured sailors are suing for alleged mental illnesses, physical maladies or both.

They are demanding $5m each, for a total of $195m.

The families of the dead sailors — all of whom drowned — are suing under the Death on the High Seas Act. They demand $10m each, for a total of $70m.

"The conscious pain and suffering of drowning and near-drowning victims is well-known to be so severe and universal that simulated drowning has been used as a method of harsh interrogation and torture," lawyers said in one of the complaints.

The two ships collided in the early morning hours 17 June, 2017, near the Izu Penninsula off Japan, roughly 77 nautical miles southwest of Tokyo.

The crash tore a hole in the USS Fitzgerald's hull, flooding one of the ship's berthing units where sailors were sleeping.

Lawyers described Petty Officer Second Class Joshua Tapia pushing shipmates through an overhead hatch as waters rose, before escaping himself and pulling others through.

The also detailed Petty Officer Second Class Rob Felderman's desperate swim to safety after jumping out of his bunk into chest-high water.

"He dove under the water, feeling for a path," the complaint read.

"Unable to find a clear path, he jumped for air and slammed his head on the piping above. He pushed his face between the pipes, finding an air pocket just big enough to take a final breath."

As he swam, he was able to make it past a hatch that was not watertight and floated upward, surfacing at the vestibule of the berthing area.

Tapia allegedly developed post-traumatic stress disorder and major depressive disorder after the crash, and tinnitus. Felderman suffered a traumatic brain injury and post-traumatic stress disorder.

NYK Line declined to comment. The Tokyo-listed company said its thoughts and condolences were with the families and that it has been cooperating with the investigation.

The 2,854-teu ACX Crystal (built 2008). In 2017, the ship collided with the USS Fitzgerald offshore Japan. Photo: chun-hsi/MarineTraffic

In the immediate aftermath of the crash, there was much confusion, with the US and Japan even disputing the time the ships collided.

The captain of the ACX Crystal, Ronald Advincula, would later blame the USS Fitzgerald for the incident, while the US claimed both sides "demonstrated poor seamanship".

But a navy investigation released that October found "numerous failures" on the part of the warship's leadership and watchstanders, including failure to follow sound navigation and basic watchstanding practices.

A separate internal Navy report obtained by the US-based Navy Times and commissioned to help prepare for lawsuits found other serious deficiencies, including indifferent and shorthanded officers, mistrust among the crew and a near-miss five weeks prior.

An August 2019 report on the incident from the Japan Transport Safety Board and reported in the Japan Times said USS Fitzgerald's watch was distracted by other ships in the area and had incomplete radar information on the ACX Crystal.

The crash led to three of USS Fitzgerald's senior officers being relieved of duty. Two faced criminal charges, though they were ultimately dropped.

Still, lawyers for the sailors and families laid the blame for the crash at NYK's feet, also citing a US Navy report. They said the crew of the ACX Crystal twice shined a signal light at the USS Fitzgerald instead of sounding five short blasts from its horn, as required by the International Rules of the Road and never attempted evasive manoeuvres.