The most significant innovation of the naval war in WWI was the use of submersible warships. Before that development, the focus of naval arms race between Britain and Germany has been on the big battleships and battle cruisers. In the early days of World War I, the U-9 sank three British cruisers in September 1914. German naval officers soon realized that submarines could also be very effective as commerce raiders.
Picture below shows the point of view from a U-boat as it torpedoes a merchant ship in the Miditerranean in 1916. Between October 1916 and April 1917, German submarines sank nearly 3 million tons of shipping in the Atlantic and British waters alone. Britain was in serious danger of being cut off from its trade routes, and was thought to have but six weeks' supplies of food remaining.
A British convoy zig-zags in the Atlantic. The only effective countermeasure against the U-boat proved to be the convoy system. Once employed, sinkings immediately dropped by one-third. By war's end, 99% of all merchant ships to or from Britain successfully reached their destinations. The convoy, together with superior submarine detection measures and weapons such as the depth charge, had won the U-boat war.
HMS Argus, shown painted in zebra camouflage, was the world's first aircraft carrier to have a flight deck along the entire length of the hull. Her design set a pattern for all future aircraft carriers, enabling wheeled aircraft to take off and land using the full length of the flight deck. The camouflage pattern was intended to make her harder to target from the periscope of a submarine.
That's why Singapore also invested in having her own submarines - see post HERE
Dragon released a 1/6 scale 12" action figure of U-boat Kapitänleutnant "Herbert" of the Kriegsmarine (German War Navy) in 2001 (pictures HERE) along with U-boat crew "Georg" (post HERE)
Dragon also released a 12" figure with likeness of American actor Harrison Ford who played a Russian nuclear submarine commander of the ill-fated Soviet submarine K-19, Captain Alexei Vostrikov from the movie "K-19: The Widowmaker (2002)" - pictures HERE
Certainly would have been nice to have a 1/6 version of Sir Sean Connery as Captain Marko Ramius from "The Hunt for Red October (1990)". Afterall, there have been many head sculpts of Sean Connery produced, the closest being the one of him as Captain John Patrick Mason from "The Rock (1996)" - post HERE