Final answer:
King George V was the British monarch at the time when the Titanic sank in 1912, and he remained the monarch when RMS Lusitania was sunk by a German submarine in 1915.
Step-by-step explanation:
The monarch on the British throne when the Titanic sank was King George V. The Titanic, the ship under comparison, went down on April 15, 1912, after striking an iceberg during its maiden voyage from Southampton to New York City. Although your question seems to mix up the Titanic disaster with that of the Lusitania, which was sunk three years later in 1915, the reigning monarch during both maritime tragedies was the same.
The RMS Lusitania was a British ocean liner that travelled between England and New York until a German submarine sank it in 1915, claiming the lives of 1,200 passengers, including 128 Americans. These events took place during the era following the lengthy reign of Queen Victoria and her immediate successors from the House of Hanover.