See how crews cleared and raised that sunken Norwegian frigate

The HNoMS Helge Ingstad sank over five days after colliding with a Greek oil tanker, but the Norwegian Navy has now raised the frigate and is looking at the options for re-floating and potentially re-fitting it. But it has taken months of effort to get it back to the surface and into Norway's primary navy port.

(Øyvind W. Olsen, CC BY-SA 4.0)

The Norwegian frigate HNoMS Helge Ingstad was lost on Nov. 13, 2018, five days after it collided with a Greek oil tanker and began taking on water. Now, the Norwegian Navy has recovered the wreck and begun salvage operations, and videos showing the process from the early underwater surveys to now have been released online.

The ship suffered severe damage and seemed to leak water in what were supposed to be watertight compartments (Norway and the ship's builder, a Spanish firm, are fighting over whether a design and construction failure led to the sinking or not). But the ship sank slowly, giving the crew some time to get a tug to push it into shallow water.

This was too little to save the ship, but has made salvage easier. Divers were sent in to collect sensitive documents and to remove the ship's dangerous ordnance, from torpedoes to missiles. Surprisingly, as seen in the video above the torpedoes were placed into what was, essentially, a modified dumpster.

After removal, the munitions were detonated in a remote location, and two large barges with cranes were moved over the wreck to very slowly raise it up in late February. It took time for the water to run out of the wreck, and salvage crews were sent in to help open hatches and valves to get as much of the water out as possible.

Now, the ship's remains are at Haakonsvern, Norway's primary naval base, where salvage operators are taking careful steps to preserve as much evidence of how the sinking played out as possible while also preserving what components might still be saved.

The HNoMS Helge Ingstad was heavily damaged in the crash and sank slowly over five days.

(Norwegian Armed Forces)

In fact, the ship could see active service once again. America re-floated seven combat ships sunk at Pearl Harbor and sent them back into the fight, and the Norwegian Navy is taking similar steps pioneered there to salvage as much of Helge Ingstad as possible.

Sensitive electronics exposed to seawater are being transferred into freshwater or chemical baths as saltwater becomes more corrosive when exposed to air. Approximately 1,400 parts have been scheduled for this treatment.

And, the ship still had some buoyancy when resting on the ocean's floor, so crews are looking for where air pockets might have protected some components from damage. And the hull itself might be able to be repaired and re-used.

In the meantime, the Norwegian Navy is in a tough spot. They maintain only a small fleet, and they had five main surface combatants when the Helge Ingstad was lost, meaning they're down 20 percent of the primary combat power.