The commercial submersible that went missing carrying five passengers while touring the Titanic shipwreck presents a "challenging" and "dire" situation for rescuers, a former Coast Guardsman told Fox News. 

"From what I understand, the vessels are not designed for long-range, multi-day excursions," said John Mixson, a retired U.S. Coast Guard lieutenant commander who was involved in long-range search and rescue missions. "So it's going to be a very, very uncomfortable, dark experience with a lot of hope and prayers."

"I would say it is extremely serious. It's a dire situation," he continued. "But on the other side of that fact, it is still considered classified as a search and rescue mission, which should give everyone hope, including the family members and friends of the people on board the vessel."

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Coast Guard crews from Boston are leading a search and rescue mission for a missing submersible that was exploring the Titantic shipwreck in the Atlantic Ocean. The vehicle was reported overdue on Sunday evening and authorities have yet to discover the location of the vessel.

The Coast Guard confirmed to Fox News that they were searching for a lost Titan submersible. Tourists can charter the small craft for visits to the infamous ship through OceanGate Expeditions, which recently announced new mission crews for a North Atlantic trip on social media.

"It's hard to say whenever you just lose total communications in a situation like that what actually happened until you find the vessel," Mixson told Fox News. "This isn't a common occurrence at all."

"Obviously, something very rapid and very tragic took place," he said.

Mixson also said a submerged rescue can be a "very challenging ordeal" and that though the Coast Guard has diving capabilities, the "Navy is definitely very capable of recovering something like this."

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The location of the search is approximately 900 miles east of Cape Cod in a water depth of roughly 13,000 feet. 

The submersible is advertised to have enough life support to keep five people alive for 96 hours, according to the OceanGate website. 

There was one submersible commander and four mission specialists on board the Titan, according to the Coast Guard.

"At this point, the presumption is a search and rescue mission, which would indicate that everyone who's in the process is still anticipating a favorable outcome," Mixson said. "Which means you're looking for survivors."

"At this point, you're still within 36 hours, I would definitely say there's still hope," he continued. 

To watch the full interview with Mixson, click here.