A century has passed since the largest and the most luxurious passenger liner, the RMS Titanic, sank on its maiden voyage after crashing with a huge iceberg mid-Atlantic in 1912.

Over the years, scores of scientists and explorers worldwide have intensely studied the causes of disaster; umpteen number of new theories have been put forward. However, none claims to be concrete and unanimous so far.

The 46,000-ton ocean liner was considered unsinkable but turned out to be the worst maritime disaster of all time. Just before the midnight of April 14, 1912, it collided with an iceberg southeast of Cape Race, five of its major compartments ruptured and the ship sank within a few hours.

It was carrying a total of 2,200 passengers, out of which only 700 (mostly first-class passengers) were saved and over 1,500 lost their lives.

Today it rests nearly 12,500 deep down the sea water, around 370 miles south-southeast of the Newfoundland coast

The Titanic was still a mystery for common people till American filmmaker James Cameron came up with a fictional film on the real-time disaster in 1997. The film received worldwide acclaim, and that's when it caught the attention of more and more researchers, as well as the common people.

Recently, on its 100th anniversary, several artifacts of the RMS Titanic found in underwater expeditions were exhibited and auctioned. Also, a Titanic memorial cruise, made by the same company, retraced the same route in remembrance of the ill-fated ship.

Here are some unseen underwater expedition images released on the occasion of the disaster's 100th anniversary.

Other detailed images of the Titanic - then and now - can be seen here. These rare images were released by the National Geographic last month.