What accounts for the sudden interest in large navies by powers such as Italy,Germany & the US when these countries had been continental in outlook
Especially when these countries had been largely continental in outlook
The main cause of this interest was a desire for empire and to be seen as major powers by the rest of the world.
In Germany, this came about largely because of Germany's unification and the later rise to power of Kaiser Wilhelm II. The Kaiser wanted Germany to have its "place in the sun" and to be recognized as a great power. In the United States, it came about because the US had taken all the continental territory it wanted and was interested in more. The US was also interested (with Alfred Thayer Mahan being the driving force) in being able to project its power around the world. It felt that naval power was the key to being a world power and being taken seriously by the rest of the world.