RMS Titanic sank on April 15, 1912. The location of the shipwreck was unknown until Dr. Robert Ballard discovered it in September of 1985. It is in two pieces over two miles beneath the ocean surface. The wreck is in poor condition due to a newly-discovered bacteria species eating the iron of the hull. It is expected to completely collapse within the next few decades.
HMHS Britannic was the sister ship of the RMS Titanic. It served as a hospital ship until it was torpedoed and sank off the coast of Greece in 1915. The wreck lies on its side in shallow water. The same species of bacteria eating the Titanic has been found on the Britannic, though the areas are limited and the bacteria does not appear to be thriving. The wreck is generally in good condition and is expected to last longer than the Titanic.
RMS Lusitania was a passenger transatlantic ocean liner that sank on May 7, 1915 after being torpedoed by a German U-Boat. The ship was carrying munitions and 128 American civilian passengers. The wreck lies on its side in shallow water and is in poor condition due to the British government using the wreck for mine testing, supposedly to hide the munitions it was carrying and to shield it from blame for the sinking.